Katy Perry John Mayer Split Again: 'Not Over Til It's Over,' Says Source

Katy Perry and John Mayer have split again.

Perry, 28, and Mayer, 35, have ended their relationship for the second time after they dated last summer, cooled off in August and reconciled in September. According to sources, the second split may be temporary.

"It's sad," an insider told Us Weekly while adding that "it's not over until it's over." The couple are just taking a break and are waiting to "see how things play out."

Another source confirmed that the split isn't permanent.

"She's leaving the window open," said the source.

Perry has been hard at work on her third studio album and it may have contributed to their temporary separation.

"They have both been so focused on work," the source added.

Perry hinted that she was experiencing some sort of troubles in a tweet on Monday.

"ATTENTION: Mercury is OUT of retrograde today. Thank GOD," she tweeted.

Earlier in the month, she revealed that the couple were on good terms. She shared with her millions of followers on the social media site that they were heading out to adopt an animal together.

"My boyfriend is taking me to a kitten shelter in his truck," she tweeted. "I can't think of a more perfect Saturday."

The couple attended the 2013 Grammys and a pre-Grammys event together.

Mayer said in an earlier interview, that his relationship with Perry was so "human" that he didn't feel as if he was in a celebrity relationship.

"For the first time in my life I don't feel like I'm in a celebrity relationship," Mayer told CBS Sunday Morning.  "I really don't. I'm not in a high profile -- I know it's high profile. It's hard to explain..."

"Doesn't feel that way to me," he continued. "And great! I'm glad. But I know what you're saying. I'm not denying it. I'm saying that for me it feels like something that's very human."

When asked if marriage was a possibility Mayer told CBS, "Of course. I mean, I'm still the kid from Connecticut. That's what you do."

Perry finalized her divorce from Russell Brand in February, 2012. Mayer has been romantically linked to Jennifer Aniston, Jennifer Love-Hewitt, Jessica Simpson, Minka Kelly and Taylor Swift.