Need to communicate

This might sound so stupid but I keep catching my boyfriend watching porn. We are expecting a baby, and we have sex every day still maybe even twice a day. I don't understand why he feels the need to watch it. It really upsets me, I'm against porn myself so I don't like watching it or having anything to do with it and he knows that. I've kept quiet for so long but last night I caught him deleting his history and it really got me angry and upset. Why is he watching it? It makes me feel insecure because I am getter bigger and even though he is with me he still feels some physical attraction to that woman.  It makes me feel like I have to compete with those videos. And I mean I know he loves me since we live together and are having a baby together. Some people may disagree and say I'm over reacting but it really upsets me and in some way feels like he is cheating mentally. It's making me uncomfortable and that I am not good enough for him. I want to talk to him about it tonight after he gets home from work but I don't know how to explain my feelings without him thinking it's completely stupid and that I'm just being a jealous girlfriend. Help!?