If Whitney Houston were alive to see this ... she'd be rollin' --- her sister-in-law just got a restraining order against the man who was like a son to her.
Nick Gordon -- who grew up in Whitney's house and married Whitney's daughter -- has been ordered to stay 200 yards away from Pat Houston -- Whitney's sister-in-law and executor of her estate.
Pat got the order after claiming she feared for her safety after Nick made threatening comments and posted photos of guns.
For his part, Gordon tells TMZ he was served with the order on Monday, but he "doesn't give a f***."
Definitely not the greatest love of all.