I'm so very sorry Marvel. The pain myself and Mr. S. experience at having no relationship with our only GC due to our son's estrangement is indescribable, and we hardly saw the eldest who was last seen at 8 months old, and have never seen the youngest.
I cannot imagine how much you must be suffering to have lost your GS that you clearly had built a close and loving relationship with.
It is very early days, although it must feel like an eternity since you saw him last, so there is still a chance that things will settle down and you will see him again soon.
In the meantime, you are not alone and I hope that you can find some comfort in the support I know you'll receive here on the estrangement forum.