Am I missing out on life?

I'm a rather shy and quiet person who prefers his privacy. But the reason why I feel like I'm missing out on life is because I hardly go out with my friends or peers. I mean I hear other people talking about how much of a great time they had when they went out or I see photos on Facebook of people drinking and having a good time with their mates and even going abroad with them. I can be sociable every once in a while but I feel like it's not enough. I mean these two girls once told me that if I didn't become more sociable I wouldn't be able to do anything like get a girlfriend or even get married.