I'm really sorry you're going through this, but please remember, this is not your fault. Own your own feelings but don't carry the burden for others. Hugs xxx

It's not you at fault in what happened, you weren't 'asking for it': and even if that were the case, that's no excuse for HIS behaviour. She will unfortunately find out at some point, when he cheats on her again, and more thoroughly. I would wait to make contact til then, if possible, I doubt there's any repairing of the friendship til she's found out independantly that he's a worthless POS

You were forced into a situation that it doesn't look like there was a "right" answer for. It's really shit that your friend would immediately take his side. And while it might feel depressing, hopefully soon you'll see this as a period of real strength for you

i lost one my best friends too

you have had a shit year