One-sided coparenting
TLDR: How do I co-parent with someone who isn't parenting, and deliberately undermines my parenting?
I'm fairly certain I've not posted here before, but I'm at my wit's end.
Where to begin? My son is fourteen, his mother and I separated in 2015, about a year after I returned from deployment. For around six months after, I didn't get to see my son-the only time his mother spoke to me was to demand funding. We went to court the following spring, at which point there was a formal visitation arrangement. Even then, she withheld visitation. Back to court in 2019, and we've had joint custody since. Legal costs ran almost a year of my salary out, but I still made sure all his needs were met. Getting access to anything was a constant fight, as she had informed the school and his doctor I had no say, no authority (despite the fact that I paid for his insurance.) Up until around 2018, she and my son live with her father and step-mother, and my son was beyond spoiled, to the point of infantilization. He was still having issues cleaning himself in first grade, couldn't tie his shoes until third. He was in school during COVID, and at the time was failing due to no one tracking his schoolwork. Even with the joint custody agreement, she has and continues to make unilateral decisions about everything. Fast forward a bit, and he's now getting ready to start high school. He's been failing classes majority of the year, and the drops in performance line up one to one with his time with his mother. Granted, most of that time is at his maternal grandparents', wherein there are no expectations, no accountability, no structure. He has openly told me he prefers spending time there because nothing is expected of him, and he gets to do whatever he likes. I found out tonight that she's having him work a "summer job" under the table with her latest boyfriend-someone I've not even met.
I have no idea what to do-I've no role model for this, as I had a neglectful addict father and a violent abusive step-father. I'm likely not as stern with him as I should be, but everytime I put my foot down, he calls his mom, she picks him up, and it all gets reset.