EXCLUSIVE

Khloe Kardashian has thrown in the towel, breaking up with Tristan Thompson after she found out her baby daddy allegedly cheated on her with Kylie Jenner's best friend ... TMZ has learned.

We're told Tristan flew into Los Angeles to spend Valentine's Day Thursday with Khloe and their daughter, True. On Sunday night he was at a house party, where we're told he snuggled up with Kylie's BFF, Jordyn Woods.

Witnesses tell us Tristan and Jordyn were all over each other ... making out. We're told Khloe found out and immediately broke things off with the NBA player ... a source tells us "she has had enough."

We're told there's little chance for reconciliation ... Khloe and Tristan are done.

Play video content 10/7/17 TMZ.com

You'll recall back in October 2017, Tristan was at a hookah lounge in Washington D.C. where he motorboated a woman and got handsy with another. The video surfaced days before Khloe gave birth, and just before she delivered he was seen on video going into an NYC hotel with yet another woman.

Play video content 4/8/18 SplashNews.com

Khloe hasn't been back to Cleveland much this season, though the 2 still remained together. She was on hand when Tristan's team ended an extended losing streak.