Ian is invested in Holly, because she responded to him. She is only a catch for Lena, nothing more.
Lena wooes her with her song writing and singing, but Ian had her genuine interest.
This is about body or soul: body of gurl assures her getting easily into anybodys pants - Lena path,
or brains of a boy charming a gurl enough she would show interest in him.
These are tropes you get to explore in here.
If we assume it's Holly's room and the sex scene is between her and Lena, it will be interesting to see which conditions will have to be met for it to happen – and what other scenarios there will be for that scene. I would assume something like this:
– Ian sleeps with Holly after the book fair: no LenaxHolly scene
– Ian doesn't go to the book fair (and Lena has shown Holly interest): LenaxHolly scene
– Ian goes to the book fair, but doesn't even kiss Holly: LenaxHolly scene seems likely
– Ian goes to the book fair, but tells Holly about him and Lena after their kiss: LenaxHolly scene seems highly unlikely, but I would still expect Lena and Holly to meet, and probably talk about what happened. Would probably be the most likely scenario for the beggining of a throuple route?
I would have liked a scenario where LenaxHolly isn't reliant on Ian in some way having rejected Holly first, but it doesn't very likely.
Edit: I do this strangely often: Write a comment, and then find out that someone posted something similar in the meantime…
Yeah, I think "Ian ignored Holly" might be the closest we get to that.
I would have liked the possibility of getting Lena to second or third base with Holly without the Ian/Holly route having to have been exhausted first.
Ian has to be here, because he is who introduces Lena and for Lena to steal Holly, it is your mingling
when you play either Lena or Ian.
How would you feel should a gurl you introduce to another gurl end up getting with that gurl and not you?
Ian has to have some sense of rapport with the gurls he fancies, they can not all be jerks to him, can they?