Cherry has fucked Axel, Lena's boyfriend behind her back while pretending to be her friend, and also in a threesome with them. She's hardly "vanilla". In fact, you have option to play Lena who is much more "vanilla" than that, never doing anything more than staying in faithful relationship with one of her two boyfriends ever. (Ian being potential third man in her life)
Well even though Lena was faithful to Axel, their relationship was far from vanilla, we know that for sure. And if you play her as a vanilla now, you are shown time and time again that is not what you should be doing.
As for Cherry, yes she did Lena dirty in the past, and that's wrong, even if Axel is a manipulative sociopath and narcissist, it does not excuse her. But none of that is of any concern to Ian, she was nothing but honest with him so far, not forcing any of the more fucked up stuff on him. That might still change, and knowing Eva, it probably will.
Plus she is written in a way where I do believe her when she says she regrets the stuff she has done in the past. When Axel says the same stuff to Lena... what he means is that he regrets she found out.