Why is my step dad such a douchebag?

My mom had covid and she's recovering. Stepdad been acting an ass for no reason. He had these 2 women call his phone then he got all in an uproar when she questioned him about it. She was looking for a doctor's number in her phone then he accused her of being sneaky then he just stopped talking to her. Then she confronted him about not speaking to him then he cussed her out and he punched her in the head, I saw and started swinging trying to get him off her. Before he packed his stuff he told my mom "next time you catch covid I hope you die". He better hope he doesn't die soon since he has surgery on his heart AGAIN.
Why is my step dad such a douchebag?
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