I can empathise with you all; we moved to the town where my daughter and 2 grandchildren live in order to support them all when ex son-in-law left (It wasn't part of our grand 'retired plan'.
However we wouldn't have missed this for the world and we have a wonderful, close relationship with both of our grandchildren.
We have been doing this for 10 years and now the younger one is going to the high school, to join his sister, in September. We'll still have them for a 'sleepover' one night a week, but 'breakfast club', when they were delivered to us at 7.40 am, has now finished!
It is important to have other things in your life that will gradually fill the gaps.
I've got another 'keen'... Ouch!