Being comfortable telling people you're gay

I'm 22 and have been in 2 longer relationships since I was 15 (the first lasted about 2 years and the other, my current relationship has lasted for 4 years and counting). I'm very proud of my boyfriend, we've lived together for 2 years now and our relationship is basically everything I'd hope for, but when I meet new people I find it hard telling them that I'm gay, and that I live with a man. Everyone generally assume that I'm straight, and I even find it hard to correct them when they do so. I think I'm afraid of being treated differently when they find out.My family and friends know that I'm gay, but how do I tell class mates (I'm in a new class right now), and other acquaintances in the future?I might add that I'm very disconnected from the LGBT community where I live.I figure I'm not alone in dealing with this, does anyone have any advice on how to become more comfortable telling people?