“Khloé was upset to find out that he cheated again,” says the source. “She just can’t believe that he is going to be a dad again.”
The insider confirms that Kardashian, 37, and Thompson, 30, were together in March when Nichols claims she was involved with the NBA star. “It’s just a sad situation to her,” they add.
Thompson is already dad to daughter True, 3, whom he shares withKhloé Kardashian, plus son Prince, 4, whom he shares with ex-girlfriend Jordan Craig.
Never miss a story — sign up forPEOPLE’s free daily newsletterto stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
Tristan Thompson and Khloé Kardashian.George Pimentel/Getty Images; Khloe Kardashian/Instagram

“She is just a really great person and wants to see the positive in people,” they say.
The insider added that the couple was “doing great” while quarantined together during the COVID-19 lockdown, but that Kardashian “knew things would change” as soon as he returned to the NBA. “She was just hopeful that he would stay faithful and loyal to her,” says the source.
“Khloe’s family always tried to support her,” they add. “They always treated Tristan well even after he broke Khloe’s heart multiple times.”
Tristan Thompson and Khloé Kardashian with daughter True.Tristan Thompson Instagram

Thompson and Kardashian have been on and off for several years, andmost recently splitin June. At one point, the former couple was exploring the idea of having another child together, but their plans for a surrogate fell through last summer. A source previously told PEOPLE that the exes are continuing to “keep things friendly” for True’s sake.
“Let me love you a little more, before you are not so little anymore#MyEverything❤️❤️,” Thompson captioned the sweet Instagram post.
Kardashian commented on the photo, writing, “They are so beautiful and sweet!!!! So so blessed!!! What angels! ❤️.”
The NBA player typically shares snaps while spending time with his kids individually. Thompson previouslygave fans a glimpseof his kids together back in 2018 after True was born, posting a family portrait on Instagram for the first time.
source: people.com