I found this interesting article. I think I’d feel the same as you do, but I would try to get to know his boyfriend. It’s not approval, you’ve already made that point, but it’s acceptance of your son as a person you trust to make his own decisions (even if you still have doubts about that!).

You can’t change the situation by staying away or “protesting”, you will only be undermining your relationship with your son. And that’s too valuable to lose just to make a point.