This! My Sperm Donour slept with my best friend a week after we broke up a few years ago. I was on the phone with her for like an hour making plans to hang out and stuff. I got off the phone to see I'd missed a call from my mom, which was to call me to tell me that she was sleeping with him. I called her back and she had the nerve to tell me it was my fault we broke up and I'm a bitch, etc. I've never been so fuming mad in my life. After months of work on me and SD's end we got back together, and swore to never talk about her again. The day he kicked me out he readded her on FB, and I found out she's pregnant. From around the time they slept together. I don't know if it's his, but omfg if it is... I can't tell you if the anger ever goes away, or if your trust ever comes back. But just remember, it's not worth your time to be angry.