The split between Nia Long and Ime Udoka is getting nastier ... the actress is now asking for primary custody of the couple's child -- after she claims the NBA head coach has been failing to support the kid.
Long made the allegation in a court filing in Los Angeles last week ... while requesting a judge give her primary legal and physical custody of their 11-year-old son, Kez.
According to the docs, however, she did ask the judge to allow Udoka a reasonable opportunity to visit their kid to the extent "consistent with the child's best interest."
A ruling on the petition has not yet been handed down. Udoka has yet to respond.
As we reported, the couple broke up in late 2022 after 13 years together ... following allegations that Udoka had an affair with a team staffer while he was the Boston Celtics' coach.
Long had said at the time that the scandal was revealed that she was heartbroken ... adding that it was all "devastating" to her and her family.
Udoka, meanwhile, has since landed a new gig after the affair led to his ouster from Boston -- the 46-year-old just became the head coach of the Houston Rockets this offseason.