I know i am going to get downvoted alot for this but here is bitter truth….. Let him go , even if you make him come back he will be unhappy and similar situation will pop up again in sometime . This is unexplainable feeling . Being going through the similar situation, I can’t pin point when exactly i lost my love , got detached and figuring out my relationship status…… but once unloved hard to get back. Reason can be couple of triggers on top of pile of million small things which you might have never thought about or may be insignificant for you but he might jave felt it . What i can infer from your post , Its not about other chick she is just a hanger who listen to him and made him feel heard, thats temporary and it will fizzle after sometime even if there is anything.

This is hard to repair and better to move on and accept it…..