Nicole and Mischa used to be really close friends, but after Nicole started a family with Joel Madden, she stopped associating with Mischa because she didn't want to be around "negative, unsafe behavior."
"In the last few years, her dark side has really come out," says the source, who is close to both Richie and Barton. "Her friends, like Nicole, want to be supportive but they really can't be around her too much. She's too volatile."
"It makes us sad, but we're also like, 'Pull it together and get help already,'" adds the source to People magazine.
The turning point in their relationship happened during a mutual pal's Memorial Day BBQ back in 2007. During the BBQ, Mischa fell ill and was taken to the hospital.
"Most of her Hollywood friends have distanced themselves from her [since that party]," says a third source. "After that happened, her friends thought it would be a wake-up call, but it wasn't."
Nicole was quite the party girl herself a few years back, but luckily, she realized she was headed down the wrong path and she quickly cleaned up her act.
Mischa's currently being held at a psych ward in Los Angeles, but we're hoping she'll come out of this with a new perspective on life and maybe even turn her life around. It's never too late!