Well, I guess I'm going to have to sound the dissonant note here.
Hara, I would recommend that you NOT do anything sexual with the guy, because (1) he is still married and (2) one must be careful about doing anything with someone from work. If you and he did take the proverbial plunge and things didn't work out, you and he would still have to navigate your common relationship in a work environment. So 'tis better to let fantasies remain fantasies and still be able to respect one another.
Besides, ask yourself: do you REALLY want to hook up with and possibly get into a relationship with a guy whom you know does not take his marriage seriously? That already tells you how he might regard a relationship with you.