IIN that I can only orgasm if I imagine my boyfriend with another girl

I'm a 22 year old female experiencing the same problem. My mother cheated on my dad when I was small, it teared up our whole family. The person she started an affair with used to come to our house and even as a child it arrouse me to imagine them having sex (doing something forbidden). This could have influenced me and my relationships, it's impossible for me to climax without imagining him having sex with another woman or getting engaged in a threesome. Sometimes I even ask him to tell me a stories about two girls and a guy. To some extend it harms my relationship but I can't think of another way to climax. Right after I've reached the orgasm, I start feeling guilty and apologize to him. I beg him not to leave. It's like a vicious cycle.