Khloe says she was reluctant to continue seeing Tristan when he confessed to a pregnant ex ... but believed him when he and his people told her he and his ex were done.

"He pleaded with me that the relationship was over before we met," Khloe says. She claims he showed her evidence ... and had her talking to his lawyer, mother and friends to convince her they were through.

"This is MY TRUTH," Khloe says, insisting she truly believed Tristan was single when they started dating ... and if he wasn't, she is "so completely and utterly sorry," but pins the blame on those who lied to her.

"I pray my truth is in fact that," she wrote. "Lord knows I pray but now, I really don't know what to believe."

Jordan Craig claimed in court documents obtained by Radar Online she found out Tristan was cheating just a month after discovering she was pregnant ... and said Tristan had denied even knowing Khloe before she saw them together in paparazzi pics.

Khloe, of course, would face a similar experience with Tristan on the heels of giving birth and after.