"My children [are] what kept me alive," the star shared.
"They're the ones that kept me fighting and wanting to live. There were many days that I really didn't want to live anymore. But when you look at your children, it's not a choice anymore. You have to get through."
Foster is mom to 20-year-old daughter Gigi Hadid, 19-year-old daughter Bella Hadid and 16-year-old Anwar Hadid with her first husband, Mohamed Hadid.
Bella and Anwar are also diagnosed with Lyme disease but don't experience symptoms as severe as their mom's.
She said the side effects caused her to change and took a toll on her marriage to David Foster, who she split from in December.
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"The patient suffers, but the caretakers suffer, too. At the end of the day, David never changed, I changed," she explained. "I'm not the woman I used to be and I probably will never be again. My focus, my energy goes to trying to get well ... and David's life is really traveling, going to concerts, loud music."
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