My best friend's dad has been in an on and off relationship for a few years with practically the same woman you're describing here. She conjures up bs reasons to hate my friend, and my friend is one of the most mature, drama - free people I know. This woman has called her every nasty name in the book. I have gotten so angry on her behalf, as have other people close to her when she vents about this woman. We've all told her to stand up for herself and cuss the lady out, but my friend always takes the high road. She recognized early on that some people are just crazy. When you're dealing with this type of crazy, where everyone is an enemy who is out to get her, and she is never wrong, and will get down right nasty to whomever she wants, you have to just remind yourself that it is no use. Whatever you say, no matter how valid your point, will never be taken into consideration as anything other than more ammunition for her to turn around on you. Every time you play this woman's game and react with anger, you've only magnified the situation. Even if you wait until things cool down and approach her with a calm tone or even plead with her to start over, she will zero in on any statement remotely critical of her, and she will lash out. The only way it will ever change is if your father grows a backbone and ends it with her. But don't be surprised if he wants to, but is afraid because of her emotional abuse and manipulation of him. A good start would be waiting for a moment alone with your dad, where she can't possibly intercept the communication and let him know exactly how you feel, and that you don't want to force your dad to make a choice, but you cannot be around his girlfriend much longer, you are making your best effort for other living arrangements, and if this woman is treating him at all like she treats you, you want him to know he can do better and find someone who respects him and his other loved ones. You can suggest counseling for him as well. Do your best not to let this lady get under your skin. Her qualms with you aren't valid. She is a deeply unhappy person because of her personality, and if she didn't have you around, she'd find another punching bag, because that's just who she is. Pity her for her nonsense rather than letting it bait you into anger.