What a sad situation.
I had an appalling relationship with my MIL for 30 years . I just wasn't who she wanted for her son. Luckily for me , she passed away and I make absolutely no apology for feeling like that. My husband never backed me up and never saw what was going on, so I understand how your DS is. After all he chose this woman , obviously loves her and thinks she does no wrong.
And to be fair that's what you want from your parter.
I think you need to skip the messages , phone calls etc and do this face to face. There can be all sorts of problems with misunderstandings with text. Be calm, apologise genuinely for any offence you caused - even if you don't know what that is. Explain how important it is for you to see the two of them start what you're sure will be a long and happy life together.
Then explain you've missed them both and obviously your DGS.
Then leave them to make THEIR choice.
You may not get invited to the wedding but you've done the right thing. If it's thrown back in your face , you will at least have the satisfaction of trying everything you could. Send a card and a gift for the wedding and be brave.
Then once that's out of the way, carry on life as normal, call and ask if they'd like to come for dinner or let you babysit DGS. Make an assumption that things are back to normal and maybe after the wedding madness they will be x