LEGAL custody of children question

After months of continuances, my divorce is just about finalized.

Last second, my ex decided to throw in that he doesn’t want me have sole physical and legal custody of our children. He is stuck on the legal part. I already have temporary sole physical and legal custody, due to domestic violence, mental heath concerns, and substance abuse issues in the past. I receive no child support. No help, at all, with; getting the children to and from school, extra curriculars, Drs appts, surgeries, Dental appts, therapy appts, psychiatry appts, EVERYTHING, I do on my own, with FOUR children. AND I work full time!

How can I prove that I have been the one doing it all for our children? Should I start a “custody” journal, journaling all of the times that I bring the kids to school stuff, medical appts, or activities? I could ask my kids PCP for a note, stating who has brought them to every appt maybe? I have a sneaking suspicion that the judge wants to see actual proof, not just a journal, from me. Maybe? Or, I could ask the hospital, and school’s social worker for a letter too?

Also- I understand that having legal custody is important, I just don’t understand why he’s fighting for it. When he has had little to no involvement with any sort of “legal” matters, with our children, what’s the point? He trusts that I can do all of the work with raising them, like making sure they’re healthy, educated and happy, but not with legal decisions? I have a feeling this is all some sort of control/power play. I have compromised my @$$ off in this divorce. I have never asked for a dime, just sole custody of the kids, and to be left alone.

Location: Minnesota