You know what I'm going to say - it's written between the lines of your Question, so I'll say it out loud, and then a non-judgemental stranger has said it for you -
Stay away, this is only going to end in tears. Treat it as a harmful work-based relationship, and find yourself some more friends outside work to take your mind off him. Another relationship with someone more suitable for you will have you wondering what on earth you saw in him.
This is a crush, and it does hurt, but he may take advantage of your feelings, just because he can, and everyone looses.
Leave it alone - you know it's best.