Hey Outrider.
I'm sorry that this is the environment you're currently living in. You mentioned that your family is moving; will your step-dad be living with you at this new place? Or is your mom planning to separate/divorce him? In your opinion, how likely is it that your mom will follow through with the plan? Sometimes, even when there is a plan in place, victims will continue to live with their abusers and if this is the case, then sadly, the only choice you can make would be to move out yourself.
Anyways, I can relate a bit to what you've written...and what I've learned is that you can't reason with someone who is currently exploding with anger. Yelling back at them would aggravate them even more. Sometimes, even talking to them in a calm voice won't even help. If you want to call the police the next time it happens, then trust your gut and do it.
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Don't settle for someone who doesn't see your worth.