I'm gonna go on a bit of a rant here so bear with me. (This is my humble opinion and I didn't explore every possibility so maybe there are routes that do make sense)
Slut Lena route doesn't make any sense, let me explain:
Robert: he's a manipulative beta, clingy af, only cares about sex and he doesn't seem to get the message.
Lena doesn't look like the type of girl that would have sex with him just so she would have sex with someone.
All and all, she said he's easy on the eye but I don't think so 3/10
Mike: It's established from the get go that Mike has a girlfriend. I don't understand why tho. Feels like the only reason he has a GF is so Lena can do the same thing Cherry did. Not very plausible in my humble opinion. Axel hurt Lena so bad that I don't think she would try to do something like that to other girl. 1/10
Jeremy: Same thing. Jeremy is Louise's boyfriend and Louise is her roomate so I'd assume it's even less plausible than Mike. I refuse to believe that Lena would do such a horrible thing to her friend and roomate. I know he's not Louise's boyfriend for long but it still sounds ver unlikely 0/10
Axel: Not a fucking chance.
Mark: Possibly, if he's not with Holly. 6/10
Remember, this is just my humble opinion. Slut Lena route can work for one simple reason. Women
On the other hand, Ian has plethora of single girls he can fuck...