Exes bm stalking and harrasing me

So me and this girl share the same ex I'm 24 and she 21 my ex is 39 ...this all started cuz i let my ex use my car like he put 20$ in my tank so of course I let him gas ain't cheap , he didn't even come inside my apartment it was strictly a business deal but for 3 days now she's been stalking me and harrasing me threatening violence, but me I'm not a fighter and if she touches me I'm going to jail I keep protection on me at all times so what can I do I was thinking about asking her to stop stalking me and threatening me so she could admit it and I have evidence on her, so I can file a harassment charge , cuz I leave my apartment she's waiting on me I'm sleeping with somebody else so I definitely ain't sleeping with my ex but I won't turn down gas being put in my car and my man had no issues with him using it because he knows that me and my ex aren't sleeping with each other.