Tekashi69's claim the tattoo artist who inspired his name used to be on heroin is costing that man dearly ... at least according to the ink master himself, who says his wife left him over that drug abuse allegation.
Takashi Matsuba spells it out in his ongoing civil suit against the rapper -- and in the new legal docs, obtained by TMZ, he says he's entitled to a default judgment because Tekashi's old lawyer withdrew from the case and Tekashi's failed to retain new counsel.
But, in re-explaining the alleged harm he's endured, Matsuba makes this startling confession -- "I lost a number of friends, but by far the most important one is my dear wife. We divorced last year, because she no longer trusted me after Hernandez's false statements about me were broadcast on Hulu and Showtime."
Matsuba goes on to explain that his tattooing business has essentially collapsed by "the false suggestion that I may be a drug user."
You'll recall ... Matsuba was pissed over a couple 6ix9ine documentaries that name-dropped him -- one on Hulu, and another on Showtime. While he seems pissed about the Hulu reference, it's the Showtime doc that's in his legal crosshairs ... they're defendants too.
The Showtime project features a clip of Tekashi telling the story of how he picked his moniker, and in describing that -- he alleges Matsuba is a former heroin addict. Matsuba vehemently denies that, and it spurred him to sue.