16 YEAR OLD STEPSON THREATENED TO HIT ME...ADVICE WELCOMED...

So I'm 34 years old and I'm in a relationship with my partner Jennifer. I'm also 14 weeks pregnant. I've gone through a lot to get pregnant including a miscarriage several years ago. I've also had some obstacles during this pregnancy and am considered high risk. Well my partner has her 16 year old son living with us who has a lot of behavioral problems. In the past month he has had several run ins with the cops, including one where he falsely reported an armed robbery, he's been kicked out of school for drugs, he doesn't do anything he's asked and when he gets punished he gets violent. Today I took his PlayStation away from him and he followed me into the bedroom and told me to give it back and started cussing at me. When I refused to give it back he got up in my face and said "I don't care if you're pregnant I will hit you." Of course his mom, like always, took his side and didn't do anything. So I've decided to leave. I don't want to but I refuse to put my child in danger and he is the type of kid that would do harm. Am I wrong in choosing to leave?