What Do I Do?

Have you ever realized that you would give anything to be with the one you love and loves you? But he's one of your closest friends, and he has a current girlfriend. One that he has been dating steady for a good two it three years. What am I supposed to do? Should I tell him? Not expecting a response? Do I tell him and hope for him to return my feelings? This my friends, is my dilemma. What do I do?