Lena forgives Ian during Chapter 9 if she's not mad at him (for fighting with Robert for example) and if you don't try to bury yourself in a deeper hole by saying it was unfair and accept that you were wrong to mess with Holly's feelings like that and that it was really inconsiderate towards Holly's friendship with Lena. Lena then understands that Ian is actually a good person, and so they start dating again.
I'm not sure I enjoy that level of ass kissing for a woman Ian wasn't in a relationship with and who has done just as much
playing the field as Ian has, and who encouraged Holly to go for it and who ignores the fact that it was Holly,
not Ian that initiated it all! I'm looking into replaying the game and ignoring Lena totally. I get too annoyed at the whole Holly thing... either that or just leave out Holly totally as that line is totally messed up and too annoying in the writing. Lena's character is definitely a huge hypocrite.
If I had to rewrite it, I'd make it so Lena blames Ian for scaring Holly away from hanging out with her, leading Ian to feeling guilty not because he "cheated" on Lena, but because he made things awkward between the three of them. Which then leads to him redeeming himself by inviting Holly to Lena's concert, which would warm Lena's heart once again, and then she'd admit that she panicked and overreacted because she can't stand the thought of losing Holly as a friend but also explain that she's now feeling guilty hooking up with Ian, given that Holly is heartbroken so it's best they take a bit of time off to figure things out. Then, once Holly heals her wounds and gives her go-ahead to Lena, she feels more comfortable dating Ian again while Holly knows unless Ian pisses Lena off somehow.
Even that would be messed up as it wasn't entirely Ian's fault! Holly liked Ian, she made that clear early on in the game when she first met Lena! She wanted Ian to come with her and She admitted to wanting to have sex with Ian
even though she KNEW he was probably with Lena, so no, it is not Ian's fault, not entirely and I hate how all of this keeps pointing the finger at Ian as being "at fault" from hypocritical woman who sleep around just as much. Also, at the time Ian slept with Holly, he was not in a relationship with Lena (or anyone for that matter)...
BOTH Lena and Ian were playing the field, and
both knew Holly for at least as long; actually, Ian knew Holly before Lena did.
Give me some story in the future where Lena apologizes for overreacting to Ian and Holly and she admits Holly was at least as much at fault and how she had no right to complain given her own actions and lack of relationship and I'll be okay with it. At the moment, she's making faces every time she sees Ian with another woman while she bangs all the guys she meets.