If on-line, just don't reply to his messages, he will understand in a little while that you are no longer interested and will move on. It's really a numbers game for a lot of me.
If off-line, on the phone,just say you are interested in somebody else and wish him luck. Then block is number and you move-on
RE: Men, I need your advice
Just tell him you have made a commitment and are no longer available.