Khloe Kardashian/Instagram Khloé Kardashian and Andrea Thompson
In an emotional tribute posted on Instagram Monday, Khloé shared her grief at the sudden death of Thompson's mother, who suffered a heart attack and died in her home in Toronto earlier this month.
"I have been avoiding this ... Avoiding accepting this is real," she wrote in the lengthy caption.
"This has been one of the toughest times in so many of our lives," continued Khloé, 38. "But at the same time, I feel blessed that I am lucky to have had someone that makes saying goodbye so incredibly difficult. So difficult that I'm choosing not to say goodbye for good because that is something I cannot fathom."
"I'm choosing to say, that until I see you again in Heaven, I miss you and I will continue to miss you more and more every single day," the reality star added.
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Jerritt Clark/Getty From left: Andrea Thompson, Tristan Thompson, Kris Jenner and Khloé Kardashian
Khloé also promised to "look after," "help" and "protect" Amari, Tristan's 16-year old brother, who has epilepsy.
"I know you never wanted to leave your boys. They are your entire world," she wrote. "They will learn to live with the hole in their hearts because they are warriors just like their warrior mommy."
Following the news of his mother's death, Thompson, 31, flew to Toronto to be with his family, and Khloé joined him, a source told PEOPLE. She was close with Andrea, the source said, as her sweet tribute makes clear.
Khloé was joined by her mother, Kris Jenner, and sister Kim Kardashian for Andrea's funeral in Toronto a few days later, a source told PEOPLE. (A separate source told PEOPLE that Kris, 67, spoke at the memorial services.)
"They all want to be there for Tristan," the first source said. "He will always be family. It's a devastating situation for him. They want to do everything they can to support him."
George Pimentel/Getty Andrea and Tristan Thompson
Kris also posted an emotional tribute to Andrea on Instagram, sharing her "heartbroken" feelings over the latter's "sudden passing."
"You were the most amazing, dedicated, devoted, and selfless mom and such a loving, kind, and fabulous grandmother," she wrote. "What a blessing you were to your family!!! I will miss you Andrea. I will miss your bright spirit and amazing light."
While the Kardashian-Jenner clan has had their ups and downs with Thompson — most recently, the NBA player allegedly fathered a baby with Maralee Nichols while he was dating Khloé — the family has showed up for him when he needed it most.
As co-parents, he and Khloé have remained on good terms. The Good American founder even allowed him into the hospital room following the birth of their son last year.
"I've been on the fence about letting Tristan come to the hospital or not, but Tristan wants to be here so I just figured, why not let him come?" she said on an episode of The Kardashians. "I'll never get this moment back."