I just don't see Seymour, as the kind of guy who shares his toys with anybody. So the idea that he's going to include Ian in his sex games with Lena, well I just don't see that happening at all. He's already indicated that he's searching for someone to leave his legacy to, and since he has no children or close relatives, the clear implication is that he intends Lena to be that person. And his sex games, are a means to mold/corrupt her, into the type of person he believes will be worthy of such a responsibility. As far as he's concerned, there's a deeper purpose to all of this, beyond merely sex.
You say this is a porn game, as if that automatically eliminates any dramatic elements that don't involve sex. If that's the case, then why do we have the MMA tournament in such depth, without any sexual element whatsoever? This isn't merely a porn game, that concentrates on just sex, with dramatic elements tagged on as an afterthought. The drama and the realistic relationships that back it up, have been carefully constructed, and are as important as the sexual elements, or at the very least more important than in most 'porn' games. And that's why this game, has such a healthy following, who feel compelled to spend hours everyday making comments on this thread.
In any case, what you're suggesting that Seymour is doing with Ian, is not something that presently exists in the game, and is more what you want to happen, despite there being no evidence that it ever will. Because the only person, that Seymour is presently doing anything with, is Lena. And Seymour's ultimate intentions for Ian, are as yet unclear. I might be right, you might be right, but we could both be completely wrong.