If he's uncomfortable at parties, don't bring him.
As for other dogs, have you tried taking him for a walk with another dog? They don't have to play or be best friends but it might help him be ok with other dogs if he's on a walk with them and he isn't forced to completely interact with them.
As for not being able to walk him because he's too strong, get a prong collar, make sure the edges are round and not sharp to the touch and put it on him. They are miracle tools!
Sinister "The Prince of Darkness" 4 yr old black male GSD 3.11.09
Draco "Dakota's Unbreakable Vow" 5.5 mth old male Dalmatian 6.30.13
Cats: Chaos, Mayhem, Monster, Wicked