The Will & Grace star and screenwriter Daniel Zelman ended their 10-year marriage earlier this year (11) and quietly went their separate ways.
But the couple has refused to alter its living arrangements for the sake of its seven-year-old son Roman and is still sharing the same apartment in New York.
A source tells UsMagazine.com, "(They) have been separated the better part of the year but continue to live together in New York for Roman."
They even attended Bette Midler's Halloween party in October (11) in matching ghoul costumes, while Messing gushed about her family's holiday plans in the Big Apple last month (Nov11).
She said, "We love to go skating at Wolman rink, and go see plays... Looking forward to putting on the snowsuit and stomping through Central Park."