My ex (30M) and I (29F) still argue about the ending of our relationship and what went wrong 2+ years later?

Background information: For anyone wondering why I am still in contact with my ex, it's because we have children together and coparent on a weekly basis. It has been more than 2 years after separation and sometimes, certain conversations still spark huge discussions and arguments about the ending of our relationship and everything that went wrong and the reasons why he left me. Why do we still do this?
My ex (30M) and I (29F) still argue about the ending of our relationship and what went wrong 2+ years later?
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