Bored With My Man

Been with my fiancee for about 4 years and the relationship is getting quite boring. We never go out and do anything fun. We have a 12 year age difference,and sometimes I'm starting to think that's the problem. I have been living in Miami for the past 5 years, and ever since I meet him my social circle has shrunk. We have NO friends, and we never go out (except maybe to eat dinner). I used to go out with this girl, but I stopped because he didn't like her. Now, I get envious when I see pictures of her and her man going out to different events having a good time. I think to myself "why can't we don that"? When I ask my man to go, he finds an excuse not to go. I even invited him to go to the gym with me, but he would rather exercise at home. I just can't see being with such a boring person for the rest of my life. What should I do?