I have to say, in the middle of my current relationship, I came out to my girlfriend that I was bisexual. She was uncomfortable at first, for fear of losing me to a guy. However, I still love her, and although our relationship has been rocky lately due to other matters (i'm not even sure if it'll last right now), we had a very healthy relationship, even with my sexuality.
Our sex life was a little different than most, but we were able to make it work. Taking sammisa's advice is a good idea. I've already told my girlfriend that I love her, but some issues prevent that love from continuing. Try to make it work, and if it doesn't, then destiny has something better in store for you. Even if you talk about marriage, kids, a house, growing old, none of that means it's going to work. Although I have to say, it makes it harder to feel like it's ok to end the relationship.