Yes, it's difficult isn't it? It might be your son is feeling you have abandoned the family and thus removed support when they have been used to having you around. Children sometimes find it difficult to get their heads round the fact that their parents want a life of their own and should have the freedom to enjoy their retirement as they see fint.
I think a clear and frank discussion needs to take place. Ask your son what he would do if a fantastic job came along in another part of the country or even abroad, if it was an offer too good to turn down? Would he say no just to be near his parents? Lots of offspring seem to think that it's ok for them to follow their dreams but don't allow their parents the same freedom.
They may not understand that the decision to move away is not taken lightly as you say you miss your grandchildren.
Old sayings with a theme 2 ( continuing *nanna8*'s thread)
Last weekend, in Rutland, the first statue in Britain of the late Elizabeth II was unveiled.