FlyingSolo - I am so sorry to hear about your situation and I totally sympathise, because I am going through something similar. This is definitely an emotionally and financially abusive relationship and you would be better, if you could, to stand back from it - at least for now. I know that it is much easier said than done, but you really need to take care of yourself and value those in your life who love you and care for you.
My eldest daughter has caused nothing but upset since meeting her now DH and is estranged from both of her sisters and has cut off all of her old friends. As in your situation, she suddenly ghosted us and then there was spasmodic contact, during which period she had a baby, which she didn't tell us about. We have seen her once in three years, for lunch last year, following which she asked if she could 'borrow' some money.
A few weeks after we transferred the money, they sent us some photos of our DGD, then 14 months old, as they said it was on their conscience, as we had provided the financial assistance. The letter also said they hadn't told us before, because they didn't think they wanted us to be involved, as they only wanted her to have good relationships around her. It was a really horrible letter and designed to be as hurtful as possible.
Since then, DD has been sending lots of photos and videos of DGD1 and DGD2, who was born on Christmas Eve. We are due to visit shortly, but DH has just been diagnosed with a serious form of cancer, so I am not sure that we will be able to go now.
To be honest, I am coming round to the view that it was better when she wasn't in contact, so at least I could and just about had come to terms with the situation. SIL has poisoned DD against her family so he is bound to do the same with the DGDs and a part of me would prefer not to be involved. I really don't want to be hurt again. DH's illness has made me see things in far greater perspective.
So my advice is to try to treasure each day and the good things in your life. Your DS may well be back in the future - I believe that he will be - but for now, just get on with your life and do what's best for you 