The couple cozied up in Chicago during Fourth of July weekend
The musicians were first spotted Friday acting casual and friendly around each other.
“They were backstage being super sweet together – but not standing too close – in a big group of friends,” an onlooker tells PEOPLE. “Someone handed her a tie-dyed rose. Katy was extremely polite, gracious and friendly.”
However, things heated up on Saturday when a picture was snapped of Perry, 30, wrapping her arms around Mayer, 37.
Mayer attended all five of the final shows – two in California, three in Chicago.
They ended the weekend together on Sunday, where they continued to act affectionate while enjoying the final concert.
“They were holding hands backstage Sunday,” the onlooker tells PEOPLE. “For a short time, they were in the pit, but then the spotlight went on them, so John grabbed Katy’s hand, pulled her out and they left.”
RELATED: John Mayer, We’re Sorry We Called Your Airport Outfit a Bathrobe (but Delighted You Read the Site!)The two singers first started dating in 2012 and endured a series of breakups before calling things off in February 2014.
But since their breakup, the couple have continuously fueled relationship rumors. Earlier this summer they were spotted enjoying a day at Disneyland and were snapped hanging out with Missy Elliott after Perry’s Super Bowl halftime show.