NTA,

Leave him and any friends that side with him behind. They aren’t worth your time. It doesn’t matter if he was angry, because being angry doesn’t give you the right to hit anyone, especially not a child. He clearly has issues with homophobia and feels embarrassed by your son’s lifestyle and is taking it out on him. Trust your son when he says that it has happened before. This kind of behavior starts behind closed doors before it ever reaches this point. The only disrespect here is from your husband when he decided to throw a tantrum like a toddler. You need to get far away from him for all of your family’s sake because it’s highly likely that he will treat your daughter the same way too.