In need of some major advice and outside point of views.

My fiancé and I have been together for almost 3 years. I was 17 and he was 20 when we started dating, and I did not know him at all when he was in high school. I've only had sex with two people, him and an ex boyfriend. He's been with 8, including me. (That I know of, anyway) Among that 8, is an ex-girlfriend's mother that he states he was raped by. I don't know if it's how he deals with it or what, but when I ask him about it sometimes he outright lies about it, or acts like it's nothing. It's always bothered me since he first felt comfortable enough to tell me because something just doesn't sit right with me. It feels like there's missing details, or he feels guilty. He puts out that he's extremely against cheating, but his friends are completely comfortable talking to him about them cheating on their girlfriends. (Even while I'm sitting right there) Sometimes I feel like he's lying about it because he feels guilty about cheating on his ex girlfriend, but won't admit it. I'm afraid to push the issue because I don't want to be insensitive or make him feel like he can't come to me, but I just can't shake the uneasy feeling. Has anyone else ever experienced anything like this? **I don't know if I'm just being hormonal (31 weeks pregnant). Please don't get rude or angry with me, I'm legitimately asking for advice because I'm completely unsure of it. Thank you for your help!