I agree with Bill3 - I have experienced relationship anxiety, and while I can understand your relationship with him would seem great to you, and probably would have looked good to an outsider, I’m pretty sure for him it would have felt much different, even if he tried to pretend to himself it was fine.
You have a different perspective than his because you weren’t anxious and insecure. If he’s anything like me, he might also have gone through a sort of pattern, maybe thinking “it will be better this time” when getting into new relationships. But obviously, his underlying issues haven’t been dealt with. Hopefully he will have an “epiphany” one day and get the help he needs. It seems at least this time he recognised and acknowledged he wasn’t able to meet you where you were, so to speak.
I’m sorry this happened to you, though. No matter the reason you were broken up with it is going to sting for a while and part of that process is trying to make sense of why it happened.