Taylor Momsen ’s opening up about the rough side of "Gossip Girl" ... saying people blurred the line between her and her character so much, she had no choice but to quit the show.

The Pretty Reckless rocker spilled on "Call Her Daddy" that playing Jenny Humphrey was straight-up killing her ... she just wanted to ditch the drama and make music, but trying to break that contract by S4 was a nightmare of its own. Getty

Taylor says the execs branded her ungrateful for wanting to leave the very show that had made her so successful -- but she pushed back hard, and eventually the writers agreed to write her off.

However, Taylor was still locked into her contract until the show ended, meaning no acting gigs until the show wrapped -- but she couldn’t have cared less ... she was ready to cha

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