AITBF for being angry at a friend for dating my ex?

Before starting, I want to say this is specifically about FRIENDSHIP, and my relation with the "friend" in question, not anything regarding my ex. I will give information regarding me and my ex's relationship, but, again, I don't want to talk about her involvement in this.

So, me and my first girlfriend met at 14, fell in love, and had a 3 year long relationship. Did everything together, had great chemistry, and everything came and felt natural to us. I broke up with her from a fear of commitment. We still loved each other, and unfortunately I didn't have the maturity to step away from her, so we kept "dating" except now broken up, if that makes sense.

Anyway, 3 months after me and her ended our official relationship, I noticed over a period of time her and a childhood friend of mine messaging each other. She told me that he would tell her I was seeing other girls (I wasn't) and that she had to move on and find someone better. He never mentioned anything about it to me, but one night while I was at hers she said she had feelings for him. The next day I talked to him about it, and laid out in front of him that I wasn't comfortable with him seeing her. He said that he wasn't interested in her and said something like "maybe I shouldn't have opened up to her" for I'm presuming his personal life. She later told me that he told her me and him weren't close (we've only known each other our entire life.., though granted it was always a bit awkward between us). Found out a few weeks later that he and her had been seeing each other for a while, dates, kissing, sleeping together. I was really furious at him, and all he could say that was really meaningful was that at some point she told him something about me that "completely changed how he saw me".

From my perspective at least, there are a few points that makes me think what he did disrespected me as a friend:

• Beginning to talk/hang out with my ex after 2 months
• Listening to her side of the break up like things that changed how he saw me, and not talking to me
• Lying to her stuff about me being with other girls, that me and him weren't close, and that she should date better guys
• That he knew the level to which him pursuing this would hurt me and chose to
• Lying/withholding honesty from me
• Knowing me and her were still in a situation/had lingering feelings and choosing to step in
• Not apologising for how he hurt me (not as in he did something wrong, but more to recognise my feelings)
• Even going for her in the first place -- a bit controversial but personally friends' exes or even anyone close to them is off limits to me

I've decided thst what he did wasn't exactly something an honest friend would do, especially one that I've known for so long, and have cut him out. I understand that people can make their own choices and I don't have say over their lives, but that doesn't mean my emotions are invalid, especially towards our relationship. AITBF for feeling betrayed and being angry at him?