This, op mentioned he’s 28 and his sister is 31 they are both old enough to deal with that, he‘s old enough to make a decision, and she’s old enough to bear the consequences of her shitty behavior.

I would just completely cut her of my life. She is a shitty person not just for the assault but for the fact that she didn’t even consider how much this could fuck up her brother psychologically. If the rationalization she made is true even in her head then she’s a selfish person who prioritized her fleeting desire over her brother‘s long term wellbeing.

She’s the one that stirred this shit not him, and tearing the family apart falls on her shoulder not his.