Disabled Adult Child, Absentee Parent Now Trying To Sue For "custody" To Get Out Of Paying Support.

Throwaway account just because it's a sensitive issue. Location is a state where parental support obligations continue into adulthood for disabled children. Sorry to be so vague.

My adult child who is special needs lives with my wife (step mom) and I.

Over 15 years ago, his biological mother walked out on us and had made it very clear, repeatedly, in those years that she wanted nothing to do with her son. I never went for support as I felt we were just better off having her completely out of the picture. I met my current wife a year or two later and she has stepped into the unofficial, non-legally binding role of "mom" and continues to be.

Last year, as my son became a legal adult, financial situations changed, between his ssi changing, doctor visits, travel, etc, I decided to finally pursue financial support from my ex. First we tried to just come to an agreement of X about of dollars. She told me to pound sand because she "gave up her rights as a parent years ago." Obviously, this isn't how the law works, otherwise every deadbeat would give up their rights. So we went to court.

During the process, it turned out her income was magnitudes beyond mine, and in the end, her financial responsibility was sizable. She attempted to appeal and it was clearly rejected.

Now, she's taking me to court to try to get legal "custody" of our son, simply to get out of having to pay support.

Now, my question here is, being that our son is a legal adult, and while mentally disabled and unable to support himself financially, he is still able to make many decisions for his own self, perform basic self care, etc. He's already made it clear he doesn't want to live with his mom. She is an absolute stranger that he has seen maybe 5 times in the past 15 years, none of which she actually made an effort towards. (Grandparents visiting and bringing him with, etc).

Does my ex even have a legal standing? Shouldn't our son get final say in where he lives? Obviously, given the history, I can't see the court siding with my ex, regardless. But I just wanted to get a little insight as to not be blindsided.

A court date has been set for the near future.