Hey Megan, well sweetie...There are only things you can do to make this better. It is not him having the issue. So try to sit back and figure out why this bothers you now? Are you going out and enjoying yourself too?
Why not join the boys, it is always fun too. If you have to worry about getting him mad, then you have answered your own question. You can try showing interest in whatever he is interested in, cars, sports, pool, whatever.... If you don't know anything about it, ask him to teach you. Men love to teach women about things as long as they listen, and don't analyze it. That is what I did when I was younger, and now I am a happy woman with many of my own interests aside from that of my mates. So maybe this could also be an answer for you.
It sounds like you may be insecure about leaving him alone. This is okay, as we all go through this stage. But try to find out why inside of yourself, and if it is him...you know what to do. Women need to be more independent in relationships, or men feel claustrophobic. It is just that we are built so differently, most anyway.
Find yourself some gal pals and have fun, don't worry about what he does, and then he may come chasing you. If you don't try you will never know.
Good Luck
Blessings