LW, you are asking for the impossible. If you want a relationship with your son, you are going to have to accept that men DO marry men, that your son is married to another man, that your son will never ever "agree to disagree" on this subject, that telling your son outright that you hope his marriage will fail was incredibly cruel, and that you royally fucked up here.
But honestly, it's been 16 years since he came out and you still don't really sound like you accept that. And if you can't accept that, then you can't accept your son. He needs to take care of himself, and it may be that he can't do that if he's in contact with you, because you have made it abundantly clear that you don't accept him and never really will. It might well be that there is nothing you can do to mend these fences. You should still get some more counseling.
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But honestly, it's been 16 years since he came out and you still don't really sound like you accept that. And if you can't accept that, then you can't accept your son. He needs to take care of himself, and it may be that he can't do that if he's in contact with you, because you have made it abundantly clear that you don't accept him and never really will. It might well be that there is nothing you can do to mend these fences. You should still get some more counseling.