Jim Carrey's girlfriend commits suicide - Reasons Why?

Jim Carrey's 28-year-old on/off-again girlfriend, Cathriona White has committed suicide. Her body was found at her residence last night after her friends called the police. TMZ reports below...

Our sources say White left a suicide note addressed to Carrey which references their break up on Sept. 24. Cathriona tweeted on the 24th ... "Signing off Twitter, I hope I have been a light to my nearest and dearest."

Law enforcement tells us they believe she died from an overdose of drugs - pills were next to her body. We're told 2 friends found Cathriona last night when they went to check on her. 53-year-old Carrey and White met in 2012, dated a few months and then split. They rekindled their relationship in May.