Why is it so hard for me to let go of small things?

Like in the past I've gotten mad at my boyfriend for doing something and we talked about it and I got over it but every now and then it comes back in my head and I can't stop thinking about why did he do it. Granted it was minor. He didn't cheat or nothing on me. But i feel like other people's boyfriends do much worse and they get over it. Why can't I? I tend to be ultrasensitive and overdramatize and catastrophize everything. So do you think I should get over small things and I'm being way to suspicious for no reason? Be as blunt to me as possible