Oh sweetie! I'm soooo sorry that you are feeling this way! (((HUGS))) (sometimes a hug from a complete stranger helps! :-))
My first "advice" would be to go to your sons wedding if it's what YOU want to do. Don't go or not go because it might change someone else's actions (I've tried that, it doesn't work! lol) The only persons actions that you can control are your own. I've learned, in my relatively short life so far (30 years) that you have to do what feels right to you. You can't be the referee between your kids. They are grown adults, and need to work out their differences on their own. If you can help them set up a time to talk, fine, but I wouldn't go any farther than that.
This is just my 2 cents, my opinion, and you can take it or leave it, it's up to you. Take it if it makes sense for you, and leave it if it doesn't make sense to you. Also, I don't know you at all, but I am here if you need someone to talk to. (I've been told I have a good "listening ear" :-)) I have had battles with depression, and have days (sometimes weeks lol) where I just have the "YUCKS"
but it always gets better.
My favorite saying, and something I try to live my life by is: "This too, shall pass" basically...it will get better.
My heart goes out to you, and you are in my thoughts.
(((HUGS))) again!
~Heather