Approaching Campus crush

There's this guy at my University who I really like but eveytime I see him I don't have the courage to say anything. My heart is always racing so fast and I don't know what to do. We just stare at each other and move on. But I know he's gay as I found out last term. I don't know if he knows if I am, I assume so? I mean I haven't publicly "come out." There are a lot of reasons why I cannot, but that is another issue. Occasionally I do see him but it is beginning to become rare. What do I say? How do I approach him before it's too late? I am not comfortable doing anything in public considering me still being "in the closet", but I don't want to loose this opportunity. I really need some advice.