My boyfriend looks disappointed

Ok so I’m 13 weeks pregnant, don’t feel sexy at all, anyway.... so last night, I had sex with my boyfriend, he asked me to get on top of him so I did, I can’t ride him properly, it seems like whatever I do is crap, all I could think about is when he cheated on me with someone a few years ago, all I could think of is did she ride his dick better and could just picture him and her, I can’t get over it even a few years later, he swears hes not cheating but I don’t believe him !!