Confused

Things with my boyfriend are going good. Over the weekend tho, I was kinda thrown for a loop. We've been sleeping together for over 3 months, but over the weekend, after sex, he says he kinda feels guilty, that he knows he should wait until he's married since it's a sin. Now I have nothing against beliefs, I just don't understand why he would bring it up now. I'm divorced and he knows I have no interest in getting married again, he knew that from the beginning. I guess I don't really have a question, just needed to get it off my chest. I don't have many girlfriends to talk about stuff with so I figured this was the next best place.