What do I do about my gfs ex and mom?

Hello everyone Well, I (M18) and my girlfriend (F18) have been doing great overall with everything, but basically her mom invited her abusive/stalker ex to her house yesterday and we have never had any issues before regarding this. Yesterday was different though. As me and my gf were leaving, he pulls up in his car. I thought I was gonna have to fight him or something to protect my girlfriend yk? I was wrong. He was watching me stare at him, but went the opposite way towards my girlfriend’s mom. They started talking and I didn’t even know who it was at first until my gf told me. I felt rage when she did. Towards her mom and obviously towards her boyfriend. Her mom doing that was uncomfortable and disrespectful towards me. I told my girlfriend I would not be coming back to her house until I am fully reassured that he will NOT be coming back. The next step in this is really asking, what should I do about the whole situation? I don’t have enough money saved to move yet and she can’t live with me because my dad is an AH. What should I do about my gfs ex and mom? Is there anything I even can do?