Sounds like your AH has managed to turn you against your sister to deflect anyone from realizing that he is in fact the real jerk in this situation. This is classic addict's behavior to isolate you from people who truly have your best interests at heart. You don't have to fall for this if you don't want to.
Your sister definitely butted in where she wasn't welcome, sure, but does it not count that she made this futile gesture out of love and concern for you? Where in your AH's actions OR words is there anything remotely like love and concern? Of course he was angry for being called out, but in situations like that, mature adults admit they were wrong before they go lashing out at the very person their actions injured in the first place.