Am I being too paranoid??

So, I'm currently talking with someone. His "ex" is a little psycho and she would do anything to have him. We've been talking for almost 4 months now and everything is perfect but, the overthinking kills me... I just can't stand hearing about her, and I'm even scared that she's gonna make something else up just to have him back. Don't get me wrong, he's amazing, treats me like a queen and I trust him, BUT THIS GIRL, I JUST DONT TRUST HER!! Am I being paranoid? I just know what she's capable of and he's really sure about me but omg...just the thought makes me sick. Do I have issues?? What should I do?