Not sure what to do

So me and my fiancé are having a hard time right now , yesterday morning he told me while I went out of town for two days to take my friend to do her test and have girl time he went to another girls house a hr away and when he got inside he realized it was a mistake to go over there and left . So he told me he got the girls number because she had some stuff to sale at the pawn shop he works at . He said He went over to her house because she hit him up while he was at a low point and wasn’t in the right mind state and also because recently we argued and I told him I hated him but we didn’t brake up or leave it was just a bad fight and forgot to mention four years ago when we first got together I broke up with him for a week to be with a old guy friend and he feels like that all still bothers him . Now he’s so sorry and texting me like crazy to not leave . It’s harder to know what to do when your in the situation and have different things that are involved like our pets that I love so much and can’t leave and our apartment . I’m already 26 and no kids I’m just worried idk what to do to fix this or not to fix it. I just try not to think about it .