Thompson, 27, was spotted spending Saturday night cozying up to an unidentified brunette at the PH-D Lounge New York City in video footage and photos obtained by the Daily Mail.
TMZ and The Shade Room then published a video of Thompson and a brunette allegedly entering his hotel at 5 a.m.
TMZ also posted footage recorded in October 2017 allegedly depicting Thompson kissing one woman while a different woman groped him at the Darna hookah lounge outside of Washington D.C.
“Tristan has been consistently cheating on Khloé,” a source alleges to PEOPLE. “He’s a serial cheater. And there will be more women to come out of the woodwork.”
It is a devastating situation for the mother-to-be, who is nine months pregnant with a baby girl.
“First Lamar cheated on her and now Tristan,” the insider says. “She’s been through so much.”
Kardashian and Thompson’s reps did not immediately respond to PEOPLE’s request for comment.
The KarJenner clan are crushed for the mom-to-be, the source says. “They are heartbroken for Khloé. They didn’t realize how deceptive Tristan could really be.”
While it’s unclear if Kardashian knew about his alleged infidelity, a source close to the family tells PEOPLE she was simply focused “on the positives.”
“As far as she knew, there were no negatives,” the insider says. “Once she made the decision to commit, she was all in and trusting.”
The friend of the family says the Keeping Up with the Kardashians star “was beyond head over heels” with Thompson.
“He was her everything. They had a life together. She honestly thought he treated her like gold, like a queen,” the source says. “[He] gave her everything, doted on her, told her how beautiful she was. To her, life was perfect. And it all just came crashing down.”
Kardashian has been nesting in Cleveland with the NBA player as they await the arrival of their daughter. A source previously told PEOPLE she plans on giving birth there, and her famous family will fly in.
“I’m with Tristan and I get my home time — cooking, being with my love, and just more of a routine,” she wrote on her app and website. “In L.A., I’m SWAMPED with work. But then again, I love being in L.A. because I get to see my sisters and my mom, and I have my trainer and the people that I’ve grown up with. So there are perks to both cities for me!”
This article originally appeared on PEOPLE