To tell you the truth DrSkipper, the situation you describe seems to be the norm amongst gay/bisexual men, at least from what I've seen. I'm not saying that gay men can't have romantic/emotional relations, but most really seem to just want the sexual relations.
Personally, my first relationship was a homosexual, sex-only thing with a good friend. Although we were already good friends, adding in the sex didn't change our dynamic...we didn't get closer and didn't act any different apart from the oral sex. So in reality, it appeared to be the same "FWB" situation you described.
The thing about relationships is that in some cases a couple becomes romantically involved which leads to them getting closer and then having sex as a means of firming up the relationship. In other cases, a couple can start by having sex or other physical activities, which eventually leads them to feel emotionally closer and then they develop a romantic relationship.
What you both need to be is honest. It's okay if you are both fine with a sex-only relationship, however if one or both of you start feeling something for the other...what are you going to do about it? It's not good to hold in the feelings and not convey them because it can lead to friction in the relationship. You may want to discuss with your partner right at the beginning what you will both do if you develop romantic feelings towards him.
Good luck.