I`m bicurious and had sex with a "straight" guy. Now what?

I guess you could call me bi, but I`m not emotionally attracted to men like women, so I go with "bicurious". Anyway, my good friend and I who played college football together got drunk and had sex. I had never had sex with a guy before because I`m only attracted to a certain type of guy (very muscular, manly acting). Now he told me he`s straight, but that he was willing to "go gay" for me if we were in a relationship. I`m really attracted to him (he is handsome, manly, is 6`2", 240 lbs of muscle, and has the best butt for plowing I`ve ever seen) but I`m not emotionally attracted to him at all. I still see him as a friend, but that I want to hook up with. How do I express that to him now that he thinks I`m bisexual? Or should I just try a undercover relationship (it couldnt go public because girls generally don`t believe guys can be bi, and I don`t want to ruin my chances with a future girlfriend).