trying to understand the whole psychology for my ex boyfriend

so i have been cheated on multiple times by my ex boyfriend, he has a dating app addiction and porn addiction. he hasn't done anything physical. the first time i found out he was on a dating app i broke up with him but he begged me to give him another chance so i did, but it didn't matter, he got on it a couple times again. he has a porn addiction, he texts those instagram girls for nudes in exchange of money. once i checked his google history and it was filled with multiple sites of "jerking off with girls/strangers online". every time i asked him for an explanation why he did this to me, he just says i don't know or that he was just looking for some validation.

i understand that people project their insecurities by doing these things but i really want to understand the psychology behind doing all this because I want to stop blaming myself that i lacked everything.