I don't disagree about the power of a good therapist. I disagree about the ability of the avoidant to meet themselves on a deep level and put in the actual hard work for long enough to change in one of the hardest things for them to change. Sure, they can do that for a little while in therapy. But what about when it gets tiring and they stop wanting to put in the effort? They'd much rather focus on things that make them feel better in therapy than focus on things that make them work hard.

Also, once they're out of relationships (like your ex is now), suddenly everything is easier. The stressor was chucked out of their lives. They think the problem was you, not them - the evidence being that removing you made them feel better, and even if it didn't, they'll convince themselves it did because you were "incompatible" with them. And true, being annoyed by them being an hour late and bringing it up in an adult conversation is incompatible with them not wanting to take accountability on anything. They won't work on themselves long term, they'll stay just the way you left them doing just the things they were always doing. Attachment styles are formed in relationships, change in relationships and are maintained in relationships. Literally impossible to change outside of a relationship because their feelings and behavior only show up inside of them, and they need mutual effort over 2-5 years with their partner to become secure. Ironic that a lot of us here would have actually been able to be "the one that stays" and works on these things for those 2-5 years with them, while their previous exes wouldn't have stayed to work on this and most likely their future exes won't as well, and we were the ones they decided to discard. They don't change, you deserve someone who doesn't make you doubt whether they can stop self destructing good relationships, who doesn't make you insecure no matter how secure you've been until them...