Maybe it's just a relief all round for them Kate13, and they are feeling happier and more relaxed with everyone as a result?
How nice that she is still so friendly towards you (although probably a little un-nerving?).
It sounds like they have parted on friendly terms, whoever instigated it, and for that you should be very thankful.
My DSs have no relationship with their father (at his behest) and the DGC have no clue about their missing Grandad....and not for the want of trying by all concerned on this side, including his parents.....sadly our split was due to another, totally evil, woman, who has forced him to forsake his entire family for her, parents, sibling, children, grandchildren...the lot!
I hope, as time goes on, that you can reconcile yourself to what has happened, and that it continues to be a friendly atmosphere all round for you all.
Good luck and love to you, your son and your grandson...hang in there, it will be ok! 