I think the reality is OP that you've really struggled to accept that you aren't your son's first priority anymore, because you have been so reliant on him for companionship and care. You don't see your other children and they don't visit you, which must be very hurtful, but you're quick to make excuses for them because they have children. But even though he hasn't had children until now, your son has still had his own life which he should have been free to live. He clearly feels that he was pressured and manipulated into being your carer when, as one of five children, care should never have been solely his responsibility (especially at so young an age).
Your hatred of your daughter in law will only ever be an impediment to your relationship with your son. You see her as the reason your relationship with him has changed, as though without her he would have stayed at home and been your carer forever. That was always unrealistic. He was always going to seek independence and his own life at some point. You blame her for everything - how he treats you, the fact that he doesn't do as much for you on mothers' day as she does for her mum, for the estrangement. But really one could just as easily say she empowered him to choose his own life and prioritise his own wellbeing.
You clearly need support and companionship and help with certain tasks, but you could never reasonably expect your son to be the sole provider of those things. I think you need to reach out to the children you do still have a relationship with and ask them if they can share some of the care. They don't live so far away that they couldn't come and spend an afternoon with you every few weeks. Have you considered speaking to your GP about whether there is any support you could access to help with travel etc?
I don't know if your relationship with your son is salvageable but if you can truly stop blaming his wife for everything, stop resenting him for moving out and living his own life, and show him that you're taking steps to be less dependent on him and more understanding of his independence, then with a long period of respectful behaviour from you, there might be a way back for you to be on good terms again.