What's the big deal?
I believe that everyone's somewhere on a spectrum of straigh-gay. I'd say I'm 95% straight and 5% gay (for the sake of argument!).
I think Lash has got it right - you don't have to act on the feelings to be defined by them in some way. I've never even kissed a man and I've kissed many more than 20 women...but I can imagine that I might, in a remarkable circumstance.
Now to the matter in hand - your friend. Only you can know how he would react if you suggested more than the "play" (flirting?) which you have done to date. Don't lose a friend just for the thrill of a one time experience, I'd say...especially if you aren't sure yourself.
Then again, this could be the start of something beautiful...
Good luck, KP