There has to be a bit more to this?
What do you mean 'not allowed to visit'? Have they said that? Do you visit them? Have they visited you?
Please don't be put off what I'm about to say but you sound like you're having a bit of a tantrum because you can't get your own way.
They haven't taken you you up on your offer for you to look after him by yourself, which as their parents it's their choice to make, they might not need the help, because of this youre saying you're not inviting them over ever again.
It's not about you, what you want, what you think is best.
Your GS is 8 months old, the clingy age, he would have to travel 45 minutes to a house he doesn't know that well, with people he doesn't know that well without his parents And stay over night. He'll no. That isn't what's best for him.
My youngest is 20 months and has never stayed a day or night away from me. No amount of sulking will change that.
Go over to a thread called 'cut out of their lives' there are grans there who would love to be in your position.
You was given excellent advice last time and again on this thread.
I really hope you take it this time.