According to the source, Kim was only in NYC for a few hours before flying back to Los Angeles, where she then headed straight to the hospital to see Kanye.
"Kim was so excited to go to the Angel Ball," the source adds about the black-tie event honoring her late father, Robert Kardashian, and his humanitarian and philanthropic contributions to cancer research. "She got herself ready for last night to be her first public appearance. It's a cause that is so important to her and she wanted to be there for her family."
The source confirmed reports that Kanye was at the home of his trainer and close friend, Harley Pasternak, on Monday, when he was convinced to go to the hospital for "his own well-being and safety." The source claims Kanye had a "mental breakdown," in large part due to his busy work schedule. Prior to his hospitalization, the "Fade" rapper had been making headlines for bizarre rants during his latest shows, and he abruptly ended his show on Saturday in Sacramento, California, after just 30 minutes.
"It was a combination of a lot of issues: stress, anxiety, paranoia. He just broke," the source says. "There have been signs recently of him just overwhelmed. He has a lot going on: multiple fashion lines, the tour, his business, being a father. And then the Paris incident also threw him for a big loop. His mother passed away this time of year. So, there is a lot going on right now. Kanye hasn't been himself for a while."
The source adds that the controversial rapper is currently in "a bad place."
"Before Paris, there were a lot of things Kanye committed to work wise that he couldn't cancel. All he wanted to do was stay home with Kim and the kids [3-year-old North and 11-month-old Saint], and he couldn't," the source says. "He realized he couldn't do it all and just broke."
ET spoke to the rapper's mother-in-law, Kris Jenner, at the Angel Ball on Monday, where she said she thought Kanye was "exhausted."
"[I think he's] just really tired, yeah, it's a grueling tour," Kris said.
"All I can see is what [Kanye] said to the public -- and that is he's tired and needs some rest," Legend said before news broke that Kanye had been hospitalized. "I think he's been through a lot lately with what happened to Kim. I think if he needs to rest, I think his fans will be patient and let him rest. He'll come back stronger, hopefully."