But you will be alone together, won't you. Not really on your own. You have each other.
I don't mean to sound harsh, it is difficult when a loved one leaves for whatever reason and I have every sympathy for how you feel.
But, as others have said, we can't live our life around our grandchildren. They don't belong to us. We can just hope for a loving relationship to continue when apart, and look forward to seeing them sometimes. And it's so easy to keep in touch these days.
And this is now an opportunity to find new interests and feel freer to enjoy them. I hope it all works out happily.