Why is it hard for me to let go of the past?

Anonymous
Hey! my boyfriend and i have been together for 7 years and i must say he hasn’t always been the most faithful. from 2015-2019, he would DM girls telling them how gorgeous they are and just recently he stopped liking and following half naked girls. not by choice though, instagram deleted his account. till just a few weeks ago he realized how toxic social media really is and how it really ruins relationships. anyway, i stayed with him regardless him DMing girls and liking pictures bc i was hoping one day he would change. i guess you can say he has right? i think so too, however, i can’t let go what was done. him liking girls half naked pictures, following them, him DMing them telling them how pretty they were. i’ve asked him why he did it, his response was he was stupid and didn’t realize how of an amazing person i am. i then asked him, how come you didn’t break up with me if you weren’t sure of us? he said, bc he didn’t want to. i love him, but i also hate him. how can a man do this to a girl? like wtf. i’ve begged him to please stop liking girls pictures and to please unfollow some bc it makes me uncomfortable, he always said no bc it was his instagram and he could do whatever he wants. to some, liking girls pictures and following them is no big deal, but i am insecure so it’s a big deal to me. I don't know what to do
Why is it hard for me to let go of the past?
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