I'm 16, and I think I'm gay, but I'm in a relationship with a girl and we're engaged. what should I do?

Im 16, and I'm engaged to my girlfriend Charlotte, who i've been with for two years, and who's two months pregnant with my baby, and who loves me, and I think I love her. But the thing is, I think I'm gay, coz last week I got drunk and ended up snogging my mate who's gay, although I've suspected I'm gay for ages. And I keep having wet dreams over the thought of shagging him, I can't stop thinking about him, I think I really fancy him. Except my fiance who really loves me, and wants to the rest of my life with me, is pregnant. I'm confused, and terrified. What should I do?