It seemed like the start of a happy family reunion. On April 16, Kourtney and Kim Kardashian and Kendall Jenner flew to Cleveland to spend time with their sister, Khloé, four days after the birth of her daughter, True Thompson. The visit didn’t last long. Just a day later, the sisters were back on the tarmac, boarding an LA-bound plane with mom Kris (who’d been by Khloé’s side since the delivery) in tow.

The trip wasn’t supposed to be so short. But tensions between the new mom and her family exploded during the visit, Life & Style has learned. Furious at Khloé for refusing to dump her cheating baby daddy, Tristan Thompson, the Kardashians blew up at her, then decided to leave. "The family has given Khloé an ultimatum: 'It’s Tristan or us,'" says an insider.

"They had a huge bust-up, where Kim accused Khloé of being a 'love addict' and urged her to get help. Khloé told Kim to mind her own business. But none of the family can stand to be around Tristan. Kris told him to his face that she was disgusted by his behavior."

There’s plenty to be disgusted by. Days before Khloé gave birth, photos surfaced of him cozying up to Instagram model Lani Blair in NYC and later heading back to a hotel with her. Video also emerged showing the Cleveland Cavaliers star hooking up with two women at a Washington, D.C. — area hookah lounge in October. And a second insider says Tristan had unprotected sex with another woman in NYC last November and again in February.

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In the days after news of the cheating scandal broke, Khloé, 33, was in tears and friends were sure she’d dump Tristan, 27. But to her family’s horror, she wavered, giving True his last name and opting — at least for now — to give him another chance.

Though they love her dearly and want her to be happy, the family "doesn’t know what to do with Khloé," says a source. "She says she’s not ready to walk away from the whole thing, and they’re like, 'What are you doing?'"

Khloé’s convinced Tristan can change. She stuck by ex-husband Lamar Odom for years after his cheating and drug abuse were exposed, and her family worries she’s falling into the same unhealthy pattern. "They’re petrified that the longer she stays in Cleveland with the baby, the more likely it is that she’ll stay there instead of moving back to LA," the insider says.

"She’s lonely, but she’s very stubborn. She wants the fairy-tale ending she’s always dreamed of and will do anything to get it." Though tensions between them remain high, Kris and her daughters still hope Khloé will come to her senses and leave Tristan.

"Her whole family wants her back home, but she’s not budging so far," says the source. "Her relationship with them is completely strained."

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