The first part of the manga is about how female on male rape is destructive and should not be excused or overlooked, I REALLY don't think it'll go and excuse female on female sexual assault like that.
Her main desire is getting into a good family, likely because her own is lacking in some form. She saw the MC's efforts to help his sister as the ideal family dynamic so she became obsessed with inserting herself into the family, probably also becoming with the MC himself in the meantime. From...
You are putting too much blame on him. He started really breaking free from his trauma when he was forced to think about it again and reconsider how it affects him and his relationships, struggling through is what worked for him so it's a natural assumption that it would work for others. Add to...