I am so very sorry that you are experiencing this Jools. It's a terrible thing to be rejected by your own child and as a result have no, or very little contact with your GC.
Maybe as Coolgran has suggested, your son feels betrayed but he needs to take a good look at himself and see that this is in part because of his own lie.
He lied to his wife by telling her, or allowing her to believe he had purchased the car when in fact, due to be being in debt which he was keeping from his wife, the car was paid for by his father.
As crazy says, the passage of time does help to take the edge off the pain but it never goes away. Christmas Eve will mark the 10th anniversary of our estrangement from our youngest son and only GC, and for all of us who are estranged, Christmas is by far the hardest time of the year.
Even the very limited time you get to spend with your GC is an opportunity to make memories and remain an active part of their lives, which may well make it possible for you to see more of them when they're old enough to make decisions for themselves .