Am i over reacting?


So me and my boyfriend have arguments here and there but it’s usually what every relationship goes through. I’ve been told by a friend that he is on instagram commenting on girls post (e.g. “Wife😋”) and messaging back on their stories, “🤤”. He makes the excuse that when he did, that it was because we were on a break or broke up. In my opinion i find it very disrespectful and it makes me look very dumb. I don’t know if i trust him as much as i did before, he won’t let me have his instagram password or anything... he also knows that i don’t answer to any guy that messages me. I don’t know if i should let it slide or do something about it, because it’s not the first time i’ve caught him.