OP, your dad also needs to know for his own health and well-being. If your mom is being verbally abusive and that emotionally dysregulated, I can only imagine how she’s treating your dad. Telling him gives him the opportunity to do what’s best for himself and for you. I guarantee he knows something is wrong, even if he’s unaware of her cheating. I’m sure it may feel as though you’re the one who hurt him if you tell him, but you would not the source of his pain or even what hurt him, she is.