Something horrible happened to my then-girlfriend and I feel so guilty

I (M21) broke up with my girlfriend (F21) of a year and a half about 2 months ago. I found out soon after that before we broke up, she had been cheating on me. First it was a few times with this one guy, then a few more times with another.

I found out a few weeks afterwards that her first encounter with this first guy was not consensual. He deliberately got her high, way higher than she’d ever been, while he was pretty much sober. She broke down completely when she told me about this. I was so angry at her already, I still am, but I still felt so bad.

Soon before the cheating started, she had been going through a really rough mental patch. I knew she was, and I tried to be there for her, but now I realize I just wasn’t there enough. I didn’t take it as seriously as I could’ve. She was suffering and I feel like I let her suffer.

Before her first encounter with this guy, his friend (who was not part of the assault at all) invited me over to be there. But I didn’t want to go. I let her be put into that vulnerable situation. I always knew her impulses are lowered drastically when she gets high. And at times she can have a harmful relationship with sex. And this guy, I always had a suspicion about him. I didn’t trust him. I knew all these things and I still chose not to be there for her. I feel like I let it happen to her.

I blocked her a couple weeks ago. I’m still so mad at her for willingly going back to him and for going to the second guy. I can say pretty confidently that I hate her. But I just wish I could tell her how sorry I am. She’s been through so much already. I was always so worried for her and I tried to protect her. But in the end I failed to and I let something terrible happen to her.

I just feel such an indescribable amount of guilt. I’ve always felt guilty about things but never like this. I’m sure this feeling will go away but right now it’s just too much