After reading all of the posts, I think I would recommend NOT telling him-- at least not while he is in a relationship. If he is happy and in love with his current partner and not the cheating type, he would probably find your confession uncomfortable, disrespectful, offensive and (if you don't know him well) a little creepy. It may make him cut off all communication with you. Depending on his relationship with his current partner, he may feel that it is "the right thing to do" to show her your confession and she might ask him to cut off communication with you as well, out of respect for her. The only way I see this turning out well for you is if he IS the cheating type (but is that really what you want?)

If this guy were one of your closest friends and you saw each other all the time, then I would encourage you to disclose your feelings because they would inevitably get in the way of the friendship. But since you barely know this guy, that doesn't seem to be an issue.