ditto to not overreacting , but you need to be cautious.
A) is he still hung up on his ex? if he hasn’t moved on, you don’t want constant comparisons
B) if he has moved on, then if he is comparing you to her , is it positively or negatively? ( some divorced couples might have split amicably, with some things working but too much not working out to stay married, who knows , it might have been a positive comment. ask him)
C) MAKE SURE B4 YOU MARRY HIM THAT HE IS NOT A ANGRY, DEMANDING PERSON. A PERSON WHO IS ANGRY AND IS A STRICT, AUTHORITATIVE ,PERSON WHO WILL NOT LET YOU MAKE A MISTAKE WILL STIFLE ANY JOY YOU HAVE IN YOUR LIFE, make sure if he had the problem that it is taken care of BEFORE marriage. promises don’t work. not because he is automatically a bad person, but because it is that important