This is a very delicate situation and I've been there myself. I've eventually ended up in bed with most of the straight friends I've had over the years, but sometimes it took months or years. In no case did it spoil our friendship.

I guess my first question is how out and open you are with this guy? Does he know that man-on-man sex is something you're interested in? If not, let him know. Then days or weeks later let him know that you think he's desirable. DO NOT, however initiate sex. If you come on to him before he's ready there's a very good chance you'll scare him off and sex will never happen. And you'll probably ruin your friendship. Let him come to you. If he's your good buddy he probably will eventually. Most of my straight friends did.