Baby by another woman

My boyfriend of 3 years is having a baby by another woman. The thing is, i left him because he cheated on me with that woman and when i left him i was 3 months pregnant with our son who has a CHD. She took pride in having more of his time because i left him but I reminded her i left by choice because i have more respect for myself as a woman. She has two children already by another man. The first time she got pregnant she aborted the baby (by my boyfriend) he got her pregnant again and now she is choosing to have the baby. This is her 3rd child before the age of 24, his family does not like her because she causes more harm to him than good. They’ve only known eachother for about 8 months and she’s already called the police on him because he doesn’t want to be with her, she keys his car in, and slashed his friends tires because he wanted to work things out with me. She told him she is going to ruin his life. and even though that’s not my problem. He expects me to stay with him because he tells me it was a mistake. Please dont get me wrong ladies i have a great head on my shoulders but a mistake happens once , anything after that is a choice. I no longer want to be with him for the simple fact that she is toxic. My question is, if i dont be with him will he be with her? Why should i care right?