I don't know what my problem is...any help?

I've been dating my boyfriend since September when college started. (we're freshman) We've been spending nearly ALL of the time we have when we're not in cl together. Neither of us have really made any friends and I understand that that is not healthy at all, even if we are happy. This semester my boyfriend decided to join a fraternity and that requires a lot of time over there. (He still even spends far more time with me than there.) And I've been feeling jealousy and sadness to the point where sometimes I even get mad at him. (I've never talked to him about it though and I don't plan to) And I KNOW I am doing something wrong. Because there is nothing wrong with what my boyfriend is doing and I understand 100% that he has his own life and can do what he wants. I just don't know what I'M doing wrong that is making me feel like this. I kind of have a history of being a loner. I don't really like many people around me at once.Yet not having friends does make me sad. If I was giving advice to myself, I'd say the best thing is to make some girl friends, I just don't know how to go about doing that. I'm pretty shy. Any help?