He does have a big say in this, and, ultimately, you have to respect that. It may be that you have exhausted all you could do to mend the breech between you and your son. I would advise that you do not set yourself up to be rejected over and over. Maybe you are making things worse by keeping up the advances toward your son. Sometimes people will be quicker to come around when we sort of leave them alone. Though you can't back off expecting that outcome.

At the very least, try to more and more shift your attention to what is going on in your own life that you can move forward on. Be very attentive to the relationships that you do have and cultivate them. If you don't have any, try to form them. You need people in your life.

I wonder if your son has someone in his life who is influencing him to reject you. That's not to say you could do much about that. But it might make things more comprehendable. If he has a spouse who dislikes you, that could be the real cause of the alienation right there.