I do think that the first post in here from Hithere, gave you very, very good advice. It is so difficult when things happen in the lives of our adult children and makes them unhappy. Our instinct is to rush to them and bring them back with us. None of this is possible at present and neither is the usually a good thing to do.
Your son and his wife are parents, they have a first duty to their child, secondly to each other and (it has to be said_) only then to you.
My daughter broke with her partner in very difficult circumstances - he took money from her and for some time she was getting people coming round saying he had used their joint house against loans he took out
They had a young child, and it broke my heart before he left, when she asked one day if she could come back to my house as she did not want to go back to hers. They were spending so much time arguing and fighting.
When he did finally go - we lent my daughter the money to buy him out of the joint mortgage, I wanted him to disappear of the face of the earth,.
My daughter thought differently, he was their daughters father, and she somehow managed to keep them having some sort of relationship. He never gave any money towards her keep, but did see her and sometimes took her out.
As the years past I realised how very wrong (if understandable), my reaction had been.
My G.daughter had a great relationship with her Dad, and some wonderful memories. Unfortunately, he died when she was 16 years of age, it was my daughter who, along with his mum, were with him in those last dreadful weeks (Cancer).
My g.daughter did not have her life disrupted when he died, as her life - in her memory - had always been just her and her mum, but she has good memories of her dad and can feel proud of him.
I did apologise to my daughter and admit to her how wrong I had been.