I think the boyfriend needs the psychologist and the cat needs a new home.
I agree with you.
If they had done this to a dog, who scratched the baby, the boyfriend would have been arrested for animal abuse and the baby taken into child services for neglect.
I'm sure the cat lovers are going to hate me for this, but the animal will have to learn who is the alpha in the house, or it will end up in the shelter and unadoptable.
Yes, the child shouldn't be pulling on the cat's tail. But, the cat has to learn that it can't attack the child -- or anyone else in the family -- without consequences.
Responsible dog owners know they have to socialize a dog, so that it knows its role in the "pack". If the dog thinks he is the "alpha", you'll never be able to discipline him and will always be in fear of what it might do.
Animals don't understand "reason". If they think they can win a fight with you, you'll never control them.