According to reports from the US, although the couple signed divorce papers earlier this year, the paperwork has not been completed by a judge which means they are legally still married.
That means, as Lamar's wife, it's up to Khloe to make decisions about Lamar's care.
A source told People: "He never signed a living will, so Khloe is making decisions for him. [It's] very stressful. She is lost."
Khloe, 31, has been by former NBA player Lamar's bedside since Tuesday night. He was found unresponsive in a Nevada brothel at around 3pm on Tuesday and taken to a nearby hospital where he was treated before being transferred to a medical centre in Las Vegas.
No official statement on his condition has been given.
The former couple have been in contact in recent weeks, as documented by Keeping Up With The Kardashians.
In a recent episode, Khloe was seen telling sister Kim: "Lamar and I loved each other deeply and I don't believe in acting like that relationship never existed. Things happened but it doesn't stop me caring about him or loving him. If I feel the need to check on Lamar that's my prerogative and I will do that. I'm still, no matter what, his friend and I care to see if he's alive for the day."
Khloe has spoken frequently about her continued love for Lamar, saying: "I will never, ever not love Lamar. I was so obsessed with him in a healthy way. He was my husband, and I still wish he was."
They married in 2009 after a whirlwind one month courtship but split in 2013 amid allegations Lamar had been unfaithful and had been using drugs.
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