OP, I’m really sorry that you are now worse off than you were before, but not at all surprised. Your conciliatory message to your son told him that you were sad and you deserved better after everything you had done for him and everything you had sacrificed for him, and then you called him cruel, and now you’re surprised that didn’t work???
As long as you are so angry and unable to see how that might have been received, I think no contact is absolutely the right decision. If and when you reach the point where you lose the anger, can consider things from his point of view and make any contact more about him rather than yourself, that would be the time to try again.
Yes, you can ‘stand up for yourself’ refuse to ‘grovel’, and tell yourself “why should I” if you like, but I can guarantee that you’ll never get your son back if you do. Is that worth it?
I’m really sorry to be so harsh, but you have had plenty of sympathy and support so far from those still estranged, and sometimes an honest view from someone with a different perspective is more useful to you.
There is a longstanding support thread for those who are still estranged, and I make no judgement on those who are in that awful situation, but this is just my contribution based on my experience of having successfully ended my family’s estrangement.