For me the problem with the first issue wasn't Starfires' sex appeal it was the odd status of her memories. What she recalls isn't clear and to many it looked like the guys were taking advantage of her. While this plot hasn't been fully explored there were tidbits and in order to explain how she hooks up with Roy I think I need to go over this first.
When Kori helps save Roys' life he's upset that she didn't say hello to him. Three weeks later the trio are relaxing on a beach when Jason talks to Roy. (*1) He spins some interesting answers to questions about Gotham, Dick and Koris' memories. Lobdell has said that Jason was lying to Roy and after reading the rest of the series it's pretty obvious he's stretching the truth during the whole conversation if not from the time he meets up with Roy. Partly to keep others at arms length and seem uncaring but he also causally encourages Roy to ask her about her past. Kori doesn't have "a goldfish memory" as some have claimed. She knows about her past on her homeworld as Jason mentions it in his narration of her (RHATO #1) then later on when she talks to Roy (RHATO #5.)
Although Kori denies knowing any of the people Roy lists we know she's lying too. First of all Jason knew Kori used to hang out with other heroes, Roy being one of them. How would he know that? Jason had no idea who Kori was or her connection to Dick until he saw the Nightwing uniforms on her ship. They go to save Roy right after staying on her island and it sounds like he's bringing it up for the first time on the beach. While spinning his spiel Jason claimed that her race have trouble recalling much about humans as they have a short attention span where Earth is concerned. It's hard to see if this is true as the closest (and most insulting line) is when Kori thinks how hard it is to tell the two humans apart. I'm not sure if that was supposed to be a joke about humans all looking alike to aliens or saying that they were more alike than they thought. She never shows confusion with them or anyone else later on. Jason says that Koris' people mainly see things through sight and smell. (*2) There's seems to be a little truth in the last statement as she picks up on a memory by inhaling Dicks' scent. But it's still uncertain if it's merely Dick she has trouble remembering (if part of her doesn't want to remember him fully) or something else. (*3)
If she needs to pick up scents to trigger memories it's not as simple as some would assume. When she recalls a memory of Dick it shows that she knows Roy since he was with them in said memory. Hence she'd likely recall all her friends through other shared memories. Plus she's with Roy in the present thus she'd be able to pick up his scent and recall who he was. Despite saying she doesn't remember her ex lovers' name she says "R'ichard" during her fight with Crux (*4) and is reminded of him when she first sees Jason. The last part is another thing I've seen brought up. Why would she recall Dick if she never met Jason before? Well a member of the Untitled said she was surprise she couldn't smell Jasons' teacher on him implying that if you spend a great deal of time with someone or some place their scent usually mingles with yours. (*5) But whatever, the point is Roy isn't a stranger to her. There's never anything in the text to show she doesn't remember him, though many believed this since she ignored him at the start. I read this as her trying to ignore the things/people associated with her past and Roy says that they were never close prior to his breakout. It's not something that last long once they start hanging out with Jason.
This may surprise some but there are some subtle things going on in the panels. As mentioned in part one Lobdell doesn't get too detailed in some of the interactions. In the first issue Roys' response to the lies Jason spins? He smiles and says "interesting." Some have taken this to mean that he was thinking of having sex with Kori but that doesn't even enter his head. Roy doesn't know how much of it is true but he's under the impression that because she's with them Kori is dating Jason. He mentions this right after she hits on him. While he might not think things through Roy doesn't want to piss Jason off. This was a guy that went out of his way to save Roys' life, someone he's not sure is stable based on rumors he heard but nevertheless a guy he wants to be friends with. Yeah Roy still has sex with Kori because she said they weren't a couple but he's worried that Jason might have seen things differently because of the things he said. Especially since Jason later rushes off and is silent on the plane ride. Although neither of those things have anything to do with his friends having sex.
Still Roy doesn't seem to buy into everything Jason says. When Jason tells him to ask about the people Kori and Roy used to hang out with he takes the challenge. She denies knowing them, claims he's boring her and changes the subject. When S'aru says he needs to collect their most cherished memories Kori shows reluctance prompting Roy to call her out on the lie by asking what the big deal is if she forgets things. Her snarky answer of only remembering important things ("Ray, isn't it?") shuts him up.
In the lull of the fight with Crux (RHATO #5) Roy promises her things will get better. She responds with a grin saying it's not the most ridiculous thing he ever promised her. His reaction? Roy says "interesting" an echo of what happened in #1. He knows more is going on than what the others are saying. After Crux is defeated Roy asks why she still has her powers if Crux said he took them away. She explains that she was experimented on while she was a slave. When he tries to give Kori some comfort over it she snaps that it's in the past and she doesn't wish to discuss it.
There's been a lot of shaming on Kori for sleeping with Roy for a lot of reasons. But here's something else to keep in mind. Kori has been on that island for a long time, maybe since her break up with Dick. When Jason babbles on how awesome meeting an alien is she remarks that she's been away from humans so long that she forgot how annoying they could be. Approaching Roy for sex isn't the first thing she says to him. They were hanging out for a while (days/weeks) before he hears about it. No she doesn't start out wanting them to be overly emotional but I doubt she'd want to rush into another relationship so soon after leaving her self imposed exile. Despite the no-strings attached vibe of their tryst they cuddle afterward. As I mentioned in the first part Roys' presence changes the dynamics between Kori and Jason. Both of them get a little emotionally distant with each other as well as Roy when he joins them. It takes them a little while to warm up around him.
Once they leave to help the All Caste Roy starts exploring what his relationship is with the others. It's been stated that he's been less than popular with other heroes which makes him overly eager to have friends. So much so that Jason thinks he's a "stage three clinger." That may have some truth into it but he's also testing his bounds. Neither Jason or Kori really do more than snark back at him. Roy just doesn't seem to know where he stands with Kori at that point. He shares opinions with her throughout the book to get a better idea about Jason but doesn't talk about them as a potential couple. Roy slowly starts to understand more about Jason though he doesn't really connect with Kori until Crux enters the picture. He gives Kori hope that their all overcome their problems together. Not long after this Roy starts getting comfortable enough to be flirty with her. It's not until #8 that he shows an interest in making things a little more serious between them.
At first he's shown as the more affectionate one not only in the group but in his relationship with Kori. He's corny, more than a little blunt but oddly sweet. She banters back at him yet seems to truly enjoy their bond. Their both protective of each other although Roy seems to be the one that worries the most. The space arc gives them more focus though it still doesn't define their relationship. Back in #4 Roy flirted with a bartender when it looked like he was only going to have that one night stand with Kori. Since then neither of them have had any other romantic or sexual interests. The pair are still sleeping together (#10.) Their trust in each other is strong enough that he was willingly captured and tortured to see a plan carried out for her. Roy seems to be under the impression that he's her "boytoy" and she believes in free love. Yet he proudly refers to her as his girl more than once.
But when he's not around Kori admits she does have strong feelings for him. (*6)
Like #5 Roy gives Kori a pep talk when she's having doubts of her mission to save her people. He's thoughtful and shows that he knows there's more going on than what she shows. Once she deals with her feelings of betrayal, and knows that she has her friends backing her up as well as her sister Kori seems more at peace.
All these relationships are still growing in the book. There are more details I haven't gone though because things are left open at the moment. Like the disagreement Kori had with Jason over not killing Crux (Roy didn't want to kill him the issue before but he wasn't part of their talk.) This is a basic look at some of the interactions in the book. Kori has only been shown sleeping with two guys in this series, Dick in her memory and Roy in the present. The only other attention she's gotten has been a comment on there being a god from a unseen person in #1, a little boy that took a picture of her (likely because she was an alien), and Crux who wanted to kill her. In fact the only other person to call attention to her body besides Roy was in fact another woman, Isabel. She was a little annoyed that her date was cut short because of Kori and her rather noticeable curves.
*1 This was one of the details that was confusing. The text (in the first issue) says"3 weeks later" at the beach but Roy says they were only together for 3 days as soon as they leave (second issue) to help Jason out. But if you want a "no prize" answer for it I guess we can assume Roy was at a hospital recovering from being a prisoner of war then went to the beach. Or you know, a typo.
*2 Kori also told Jason that her people can pick up information through skin to skin contact. I don't think this was ever been fully explored prior to the relaunch but it also means they might know someone through touch. They could take in other information besides their own memories of the people they met.
*3 When the trio give up their cherished memories to S'aru to enter the room of All he mentions how unusual her memories were. "Almost impossible" to unlock though it should be noted he's not used to dealing with alien memories. In fact he uses that as an excuse to look into her memory in the first place since the rules never mentions aliens. In case your wondering no, her most cherished memory wasn't of Dick, it was of her keeping her dignity as a slave and remaining strong.
*4 And even though she's not near Jason or Roy she doesn't suddenly forget them just because their not around. There's nothing to remind her about Dick when she fights Crux (except perhaps the words he uses or his bat like shape) so I think there's more going on than we're shown.
*5 Kori does flashback to a memory of her and Dick when she's with Jason. So my theory of scents mingling might be true or only knowing people though sights/smells isn't entirely true. The latter only came from Jason when he was misleading Roy so it likely isn't anyway. And yes Kori says to both Jason and herself that she knows he isn't Dick. There's no confusion there.
#6 This has nothing to do with the text it's self but rather the picture of Kori talking to her first mate. Just so you no there is nothing sexual between them. It's actually a sweet friendship as Depalos' race are in pain when they have physical contact with other beings. He knows it means a lot to her to be comforted by such means so he ignores his own discomfort to make her feel better by touching her arm or giving hugs.