This chick is nuts!!!?

Okay I have been with the same guy for over 3 years now. We have spent almost every single day with me unless he is working. He don't have time for another female nor does he want one. My problem is his ex from over 8 years ago will not leave him alone. We changed his number cause she was always blowing his phone up. Then his freaking friend gave her his number again...I cant stand her at all she has always gone after guys I've dated which I don't care about that much it's just her trying to mess with my man. He is nowhere near interested in her at all she literally looks like a hippo now she use to look good back in the day when he dated her. She has a kid now about a year old and every time he is mean to her or pisses her off she threatens to take him to court about that kid. I know that kid isn't his she don't look a thing like him and at the time she conceived he was always with me cause he didn't even have a job then. He's not afraid of going to court over that cause he knows and so does everyone else that her daughter ain't his baby. He just doesn't want to pay for a DNA test on a child when he already knows the answer. That's $700 dollars for the DNA test and then he has to have money for a lawyer and all that stuff. I really just wanna kill the chick anybody help me find a way to deal with her before I do something stupid. Please and Thank You.