My boyfriend is cheating on me cause I don't wanna try anal?

I'm 18 and white. My boyfriend is black. I think some black guys (mostly jocks and some rappers) are hot but I had reservation about dating them. I'm not a racist but I just want someone who respects me. This is my first non-white boyfriend. Anyway we been seeing each other for like 3 months and he's mad at me for not going out of my comfort zone and not adventurous enough for him. I sleep with him alot but I don't wanna try anal and I don't think I ever will. I heard horror stories from my friends. Plus I don't get turned on when guys slap me around and stuff (don't like anything rough) so I don't let him do it. I mean I'm okay with playful slapping on my butt and stuff but he wants to do it harder and "get a reaction" or whatever he calls it. Anyway he's unhappy about our sex life and he's always telling me how much fun his friends are having. Last night I went to his place to surprise him (I have key) and I busted him having rough anal sex with some trashy Mexican who doesn't even speak English. I told him I never wanna talk to him again and left. He didn't even try to stop me but he's been texting me all day apologizing and I haven't texted back yet. Is it my fault or his fault? Am I too uptight? What should I do?