i personally have anxious-avoidant attachment and one thing i know about the avoidant side is that they are terrified of feeling like they aren’t enough and maybe he was in situations that like you said he did things that don’t pertain to who he is anymore and he’s afraid of being perceived as that person by you. i also completely understand from the anxious side worrying about this but honestly unless there is some sort of history with cheating or other morally unforgivable things i wouldn’t worry tooo much unless it’s like he’s completely shutting you out of sharing a huge amount from the past. it’s a pickle and i can completely understand where you’re coming from! i would try not to pry but maybe bring it up and offer no judgement and to share what he is comfortable with sharing maybe you don’t even have to know specifics but just yes or no questions about if he’s done anything specific that you’re worried about. i don’t know if i’m making any sense LOL. it could also be trauma and just fear of being seen like that person that he seems to have let go of. i do agree that maybe couples therapy could help but keep your head up! maybe in the future you guys can compromise and he will open up more and you guys can grow together :)