Why is it so hard to jump in and fuck a friend's ass? you understand me right?

My friend and i have known each other for a long time. we have always had a lot of filin and our relationship was one of looking and not touching until a few days ago. i don't know what happened to us. maybe the heat, a few more drinks or why not call him by his name the desire to fuck us like crazy, to put my fingers in his ass ...... to feel his cum slide down my body.