Judge to Stephon Marbury -- You Owe Your Mistress $330k in 'Hush Money'

Married ex-NBA star Stephon Marbury learned the hard way ... if you promise your mistress a boatload of "hush money" in writing ... you will HAVE to cough up the cash, this according to a NY judge.

Long story short ... Marbury struck a deal with Thurayyah Mitchell -- the personal chef he banged back in 2006 -- to keep quiet on their love affair, in exchange for a $900,000 payday. But Marbury stopped making the payments in 2010 -- after shelling out about $600,000.

Mitchell was pissed and filed legal docs demanding the rest of the cash. Marbury refused, in legal docs of his own, claiming her filing was a breach of their confidentiality deal.

On Feb. 1 the judge sided with Mitchell -- and ordered Marbury to pony up the remaining $331,584.50 he owes ... plus interest.