Mil, you need to grow the fuck up, wind your neck in and stop having a fucking tantrum like a spoilt little brat every time something doesn't go exactly your own way.
Walking out of the house on ds's 5th birthday, purely because my parents (who both work shifts and hardly ever have a weekend off let alone both at the same time) took him out the weekend before and were also there for his birthday is, quite frankly, the most appaling and childish behaviour. tip of the iceberg
Your son is an adult with his own family and you are not his number one anymore, that is his son.
You also need to remember that ds is your grandson, not your son. You don't get to make up for your own inadequacies as a mother by ignoring me, ignoring decisions made jointly by dp and I, and generally being incredibly rude.
You also need to remember that ds has more than one grandparent, and your own previous atrocious conduct has meant that my parents, who have only ever tried to be pleasant to you, are unwilling to spend any time in your company. So for things like Christmas he now gets less time with you.
On top of all of this, your behaviour is hurting your own son. How can you be so fucking selfish? I cannot begin to imagine.
If you don't change your tune and soon, you will end up pushing everyone away and you will end up old and alone like your own mother with less than ten people at your funeral. And you will be fully deserving of it.