Most Helpful Guy
That's inappropriate, period, but especially since you're a minor. Problem is, even if they were confronted with the evidence, he'd probably claim he was hacked or it was someone with the same name.
I personally wouldn't feel comfortable living in the same home with him and would contact the police if your mom stays in denial, but I Can understand that you wouldn't want to make this guy angry. Really your mom should kick him out.
Most Helpful Girl
Show her. Do not give a single thought to “how he will feel” or “how your mom will feel” because she should put you first especially when it comes to who she dates because it can put you at risk. What a shitbag.