Mom problems

I'm 19 about to be 20 I'm a college student with straight As and I have a job. A few years ago my mom caught me and my boyfriend having sex and she got really mad. Years later she still brings it up. Sometimes my boyfriend comes to see me while I'm at school, my mother immediately knows that he was there and I didn't have to say anything. She's always in my business and if my boyfriend doesn't come to my house sometimes because he's busy with work or something she says he's cheating on me. I need help because my mom really doesn't understand how much that hurts me when she talks like that and it sucks that I can't talk to her about it without her getting mad.