AITA for wanting to reconnect with my (27F) friend (30M) after he broke my friend’s (28F) heart?

Let me give you a little bit of context. For the story’s sake, let’s call my guy friend Nate and my girl friend Amanda.

Nate and I met in undergrad. He saw me through chemotherapy, intense depressive episodes, breakups, and the lot. I thought of him as my best friend at one point and he was nothing but patient and caring to me (as in he’d bike 45km to my house to bring me ice cream). We were friends for around 3 years then I met Amanda through Nate. They were in a toxic situationship for 3 years but I never really knew of her until COVID. Long story short, he was extremely avoidant and she was extremely anxious (we all know how that goes).

So for a year, we all hang out with each other online through gaming and studying on discord. She was accepted into our group with no problem. I get closer to Amanda over that year then their “relationship” started to fall apart. That’s when I started to hear about their problems through Amanda. I’m talking screenshots, and Nate was saying things like he doesn’t think he can ever love her or that she’s overly anxious and “crazy” for his liking. She would make fun of him when we’re all out together and he’d get mad at her for embarrassing him. So yeah, I was surprised because I had introduced him to all my girl friends and he has NEVER spoken to me that way. We would actually have really good banter so I didn’t think he’d be the type to get mad over her banter towards him. Amanda says that their agreement was that they’re exclusive. Then he goes and starts dating someone else. Amanda starts calling him a cheater and telling the whole friend group to cut him off.

To say I was surprised is an UNDERSTATEMENT. Like what? I was so conflicted with giving him the benefit of the doubt and with cutting him off because 1) he was one of my closest friends and 2) I just really couldn’t believe it. But seeing the things Amanda showed me honestly really disgusted me and I knew that I had to at least start distancing myself because I didn’t think I wanted to be friends with someone who could talk to anyone that way.

THEN!! Nate asks me if we can have lunch because he has to explain some things. Because he’s always been a good friend to me, I went and heard him out. I called him out for how he was speaking to Amanda and he said that he has been harboring really bad resentment towards her and that he shouldn’t have said all those things to her. He then showed me all HIS receipts 1) they were not exclusive and he repeatedly told this to her during their entire situationship. It was purely casual for him 2) he did try breaking it off but she would beg him to stay 3) his hard words usually came AFTER he would repeatedly ask for space so he can think because he doesn’t want to say anything he’ll regret and she’d force him to talk anyway. She would say things like “oh yeah, okay so you’re just using me for sex then”