'Orange Is the New Black' Star Pablo Schreiber -- Wife Fed Up ... Files for Separation

Single is the new married for Pablo Schreiber -- who plays the corrupt drug-peddling fellatio-soliciting correctional officer George Mendez on "Orange Is the New Black" -- because TMZ has learned ... his wife just pulled the plug on their marriage.

Jessica Schreiber -- a yoga instructor -- filed for legal separation shortly before Christmas -- bummer -- citing irreconcilable differences.

Pablo -- whose nickname on the show is "Pornstache" -- married Jessica in 2007. They have two kids, a 5-year-old son and a 22-month-old daughter.

Jessica isn't going easy on Pablo either -- she's demanding full physical custody of the children, and she wants Pablo to pay her spousal support. She also wants the judge to reject any bid he might make for spousal support.

Nonetheless, Jessica says she's open to giving Pablo visitation and she's willing to share legal custody. Sounds like something even Pablo's brother, Liev, can't fix.

Even though it's separation, it sounds like divorce is on the horizon. Check out his tweet a few weeks back.