My two cents:
Not only did Haley open up her legs for the MC, she opened up emotionally. She told him her deepest, darkest secret. When people are intimate, and they trust their partner, this tends to happen. I'd hate to see some of you react irl to somebody sharing their secret with you. "What happened? Get the f**k out of here with that nonsense! You just ruined my day!" (Yes, I know. This is not real life. You're here for the escapism.)
It's a tonal shift, so not everybody is going to like it. Can't argue with that. But, that's what drama is about. It adds drama! Just look at this thread.
Haley's growing out her bush! That's a win in my book!
Since people lose their minds over everything, the mods should add the tag "Plot twist." So nobody can ever be surprised by anything, ever again.
In summary:
Banging your twin sister: Normal!
Twin sister was possibly groomed by a predator, which could explain her (by society's standards) messed up infatuation with her twin brother: GTFOH!