I like the way you think, motherfuckerQuick question for the experts here: what is the most attention or dates you can have between Ian and Lena (from both sides), that would not result in automatic sex? It seems the game will lead you to them eventually having sex even if you play it fairly "friendly". My goal as Lena is to lead Ian on as much as possible, maybe a kiss at most, while slutting it up with everyone else, and have Ian stay virginal and fall in love with Lena. It seems that's not possible, as I always avoided any kisses or anything too warm as Lena, and as Ian actually, but eventually they still ended up having sex?
You can't really do this though. This game generally has realistic characters and interactions. It's not your typical tropey NTR. To not have sex, you need to avoid kissing him, avoid picking choices that make them like each other, avoid going on dates, etc. But this means Lena won't be flagged as having interest in him or dating him. It will not progress to a relationship and they just become friends.
Just give them a nice romantic relationship. It makes the betrayal sweeter after they finally "commit fully" and become an official couple (chapter 9). As Lena, you can flirt with Jeremy as much as you want, but don't actually have sex with him (chapter 8, going into Louise room to wake him up) because that prevents Ian and Lena going official. Every other character, you can bang no problem, at least so far.