In all honesty ESH.

The boyfriend sucks for obvious childish reasons.

Your sister sucks for blowing up at you and taking a rather harsh and childish stance ‘you hate him, you hate me.’

And you suck for taking words she said in distress and anger to use against her.

If you continue this you may lose your sister to a baby man and become one yourself. If you are too stubborn to have a relationship with your sister whilst she is with him then use your words and tell her why.

It’s perfectly reasonable if you don’t want to be around a man that disrespects your family’s kindness and throws a tantrum when things don’t go his way.

But chances are he does the same thing to your sister. Ask her if this is what she wants too.