My "friend" did something bad

(Trigger warning)

I just found out that my friend (using this term loosely) of 3 years repeatedly sexually assaulted his girlfriend and tried to rape her. I don't even know how to process this. I thought I knew him better. He keeps asking me to be on his side. He keeps denying everything but there's an overwhelming amount of proof going against him. I don't even want to get into that proof right now because I don't want to think about it anymore.

(I'm going to call my friend D and his gf S for clarity)

This morning when I got to school S was sitting on the ground crying hysterically and her friends were all yelling at D. I had just stepped into the courtyard and been awake for 25 minutes tops (I live close to school so I get up as late possible) and I was not prepared for any of that. I don't think I've ever been so overwhelmed in my entire life.

I've known S for a while too (ig we're friends) and I know that she's Christian and wants to stay a virgin until she's married. D is the opposite. He wants to hook up with anyone and everyone all the time. This was his first actual relationship. I'm wondering if he just couldn't handle not having sex 24/7 because that's what it seems like.

He used to make fun of S for being so religious and it started off light but then apparently turned into him shaming and pressuring her. That's what she told me today. I have no clue why she ever wanted to date him. I remember a few months ago when she told me she had a crush on him and wanted me to help her get him. I helped her. Maybe I shouldn't have but I didn't think it was my place to tell her that they weren't a good match. I mean if she liked him, what could I have done? I didn't want to annoy her. I told D that she had a crush on him and that he shouldn't date her fr if he was going to be an asshole. He has a history of being an asshole sometimes. I thought that was just a part of him, not all of him. I didn't think he was this much of an asshole. I didn't think he'd do that to her.

Now I'm thinking of everything he's ever done or said I'm the past and things are starting to add up. I hate it. I feel betrayed even though he didn't do anything to me. I thought I knew him. I thought he was a better person than this. I'm even thinking about things that S has said and done. Things I should have noticed, but didn't. I feel like this is somewhat my fault. If I hadn't helped her get with him this might not have happened. I just didn't know. I feel guilty. I hope S is okay and I don't want anything to do with D. I'm disgusted, mad and disappointed.

I want to be there for S and give her support but idk if she's even going to want to be around me now. I'm a boy so I feel like she wouldn't right now. Does that make sense? Like how some girls don't want anything to do with men after something like that happens. I really hope it doesn't fuck her up for life or something because she's such a sweet person. And I hope she doesn't blame herself.