I say this because it is better to encourage him to have a relationship of some kind with his father; it is good for both of them and perhaps they can begin to heal. Who cares about OW except as a sort of puppet in X's drama. I'm not saying force S to go, but try to soften things a bit. It is for S's sake.
Also, instead of getting offended w/X trying to tell you what to do, what if you just make a joke out of it? Come up with some one-liners there.
I wouldn't take anything X says too seriously. He's probably bumbling along trying to do what he can here and it's a lot of misguided attempts to get back into S's life.
Assuming you mean it, you could tell him you are just glad that he is trying to have R w/S.
Although I could hardly blame your poor son for being so very disillusioned w.X, you really do not want X to get out of your lives again. Your S is going to need him.
Also, if you are going to have a better coparenting R w/X, see if you can let go of the anger. You can do that better if you continue to keep your contact w/X to a minimum.
M: 16 years Bomb 4/07 OW 20s long gone Divorced 11/09 I remarried New Guy Cooperative r w/X regarding D