Just want options

Long story short my ex is with my used to be best friends. We knew each other seen we were 3 years old. The way things went down was not good so we not friends anymore. Do y’all think I should rekindle my relationship with her? I have a daughter with my ex and now they have 2 kids together an weather I am mad at her or not she will be in my daughter life an just want advice. I still care about her but at the same time I hate her for how the whole situation went down