Boyfriend has been acting distant and not attracted to me since I've been pregnant

My boyfriend and I are expecting a baby in a couple months and within the last 7ish months we have maybe had sex ten times if that . Sex of course isn't everything, but he is just acting all around distant . We are usually a very sexually involved couple , he used to cuddle a lot more , kiss me , etc . He constantly turns me down , which he never would before . I'm starting to think it's not just because I'm pregnant . I have recently caught him messaging several girls and getting attention elsewhere . I also have noticed that he watches a lot more porn . I've never been the type to feel insecure like I do now , but the more distant he becomes , the worse I feel . What should I do ? Has he lost interest in me ? I'm expecting soon and I feel like I'm wasting my time with someone that doesn't act attracted to me. Everytime I talk to him about it he gets upset and tells me that he is attracted and that nothing has changed.