The couple dated for six years but split back in July 2008.
They reunited last fall and have been seen out and about together for the last few months.
"Sarah initiated the split this time," a source tells Us. "He’s bummed."
OK, why couldn’t this apparently perfectly matched comic couple make it work?
Does that leave any hope for the rest of us?
What’s your theory on why Jimmy and Sarah went belly up again?
Was it too much to have your significant other working in the same field?
Related Sarah Silverman and Jimmy Kimmel posts:
Photo: Jimmy Kimmel and Sarah Silverman at the GQ Men of the Year Awards in 2008. Credit: FilmMagic