When the relationship loses it's conversation

My boyfriend and I have been going out for 2 years now. We met in gym class by our 1 friend. We started out as friends and a year and a half later we decided to go out. It was great. we were virtually inseperable. We talked about everything from the mundane topics like our likes and dislikes to conversations our lives and about about sex, abortion, children and other issues. But now it seems that we just talked about anything and everything and there is now nothing to talk about. We've fallen into a routine of havimg sex and watching tv while my boyfriend would spend most of the week with my one friend doing everything with her. Now beforehand he told me how he had feelings toward her (including sexual ones) and if we hadnt started going out he would have asked her. I'm a very pessimistic and shy personality. Hearing this made me feel very insecure and I kept growing like this. I've gotten pissed off at him and with drew from him. I never had a reason to distrust him and I know he would never do anything with anyone else. I don't want to break up but what do people do when the conversation dies out?