The on-again, off-again pair were photographed together again on Tuesday night, where Mayer celebrated his 35th birthday with about a dozen pals, including 27-year-old Perry, at downtown NYC eatery Freeman's.
Decked in a ladylike floral dress, Perry sat right next to the birthday boy during the low-key meal, which went on for several hours; Mayer's dad, Richard, was also on hand for the night.
"It was a very tame and civil," an eyewitness tells Us Weekly. "They talked and laughed but nobody got crazy. Everyone looked like they were having fun. John seemed happy."
Adds another observer: "John had a great time. He's matured."
Before Tuesday's festivities, the twosome were spotted spending time together in the Big Apple over the weekend: Mayer supported Perry during a private concert at Best Buy Theater in NYC's Times Square on Sunday, followed by an intimate dinner at Pearl Restaurant and cocktails at Soho House.
Mayer first began dating the recently divorced "Wide Awake" singer back in June. But after a couple months of casual dating, the two parted ways in late August. "She is making it seem like it wasn't serious with John, but she is hurt," a source told Us at the time.
Now reunited, a source explains to Us that Perry "believes she can change him."
This article originally appeared on Usmagazine.com: John Mayer Reunites With Katy Perry to Celebrate His 35th Birthday