Though John Mayer and Jennifer Aniston were decidedly mum about their romance, the singer is opening up about their breakup.

“There’s no lying, there’s no cheating, there’s no nothing,” Mayer told reporters Saturday about his split with Aniston after working out at an Equinox Gym in New York’s SoHo neighborhood.

So what went wrong? “People are different, people have different chemistry,” said Mayer, who appeared emotional, nervous and sad. “I ended a relationship to be alone, because I don’t want to waste somebody’s time if something’s not right.”

Sources confirmed that the duo, whose whirlwind romance began in April, mutually decided to split earlier this week.

Since the breakup, Aniston and Mayer have settled into their separate lives on different sides of the country.

Jennifer Aniston, showing no outward signs of grief over her breakup with John Mayer, got a pleasant surprise this week when she ran into Friends pal Courteney Cox at an L.A. restaurant.

“It was a pretty amazing scene. Jen was sitting at a table inside and then suddenly Courteney Cox walked in,” says a fellow diner at the Sunset Towers hotel’s restaurant Thursday night. “They were pretty surprised and excited to run into each other.”

Both appeared to be having business meetings over dinner, the diner says.

“Jen looked incredible,” says the diner. “Let me put it this way, it made me doubt the breakup story, because there is no way she was blue in any way. She was really happy … There was no hint of any problems.”

Aniston has been spending time at her home in the Hollywood Hills, where she was visited several times by friend and yoga instructor Mandy Ingber.

Mayer, after arriving in New York on Thursday morning on a break from his current tour, kept an even lower profile. He is due back on tour in Charlotte, N.C., on Aug. 19.

The couple, who had been dating since April, split mutually, according to a friend of Mayer.

“They were going in different directions,” says the friend. “He’s at the height of his career and very focused. Different things are important to them both right now.”

• Reporting by BRYAN ALEXANDER and MARY MARGARET

Jennifer Aniston and John Mayer have called it quits, multiple sources confirm to PEOPLE.

“They had a great time together but they are just in different places in their lives right now,” says a source of Aniston, 39, and Mayer, 30, who kicked off their courtship in April.

A friend of Mayer adds that a reconciliation isn’t necessarily out of the question: “He never ends things with a clean slate. He likes to dwell on these relationships and sort everything out before saying goodbye for good.”

Reps for Aniston and Mayer have declined to comment.

• Reporting by K.C. BAKER and ALYSSA SHELASKY

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Jennifer Aniston had a late private lunch with musician John Mayer in a Miami restaurant that opened Friday afternoon just for them, and then the couple spent a lengthy dinner together Friday night.

When it came to lunch, “I was happy to accommodate them,” says Charles Bell, general manager of Michael’s Genuine Food %26 Drink in the Miami Design District, which opened its doors for the pair early at 3:30 p.m. for the 90-minute meal.

Sitting across from each other in a booth, their heads were close together, and they were engaged in a private conversation, says Bell.

“I can’t speculate on what kind of meeting it was but they looked happy and seemed to have a great time,” he says.

The same also seemed to be true later in the day, when the two were seen at Casa Tua on South Beach.

With his arm around her, Mayer, 30, and Aniston, 39, left the restaurant a bit before 1 a.m. When they returned to her hotel, they were observed holding hands.

“We are very discreet here,” the manager of Casa Tua told PEOPLE after the two had departed. “That is why we have celebrity guests.”

The sighting was first reported on a Miami Herald blog.

John Mayer’s newest roadie - Jennifer Aniston - has been a welcome addition on his tour, say his pals.

“John has such an amazing crew of musicians and friends with him. Everyone gets along and is drama free and Jen fits right in - perfectly,” says a Mayer friend. “Everyone really loves her.”

At a recent concert in Chula Vista, Calif., Mayer’s girlfriend continued to be the subject of fans’ anonymous text messages that were displayed on twin screens between acts. One said, “We want Jennifer Aniston to come out now!!!”

Though continuing his less talk, more music approach to his concerts, Mayer rehashed his concerns about recent media coverage of his tour.

But even if the media coverage is exhausting, the source says Mayer, 30, is happier than ever with Aniston, 39.

“They are very happy together, it’s working really well and they’re only getting closer,” says the Mayer pal. “His friends think she’s great for him.”

• Reporting by VANESSA DIAZ

Jennifer Aniston, Scarlett Johansson and Charlize Theron are among the A-listers who signed on for the Stand Up To Cancer telethon in September.

American Idol David Cook, Christina Applegate, Meryl Streep and Sally Field also will appear on the Sept. 5 broadcast, which will be simultaneously aired on ABC, CBS and NBC to raise money for cancer research and treatment.

Dozens of other celebrities and sports figures will also be appearing on the program, according to Stand Up To Cancer.

It’s official: Jennifer Aniston is a John Mayer groupie. After trekking with him to shows in Michigan, Wisconsin and St. Louis this month alone, she put in another low-key appearance Sunday night in Irvine, Calif.

Early in the two-hour show - while Aniston looked on - Mayer prefaced a cover of Tom Petty’s “Free Fallin’ ” with a bit of detail about his plans for the evening.

“Just like me, this song gets to sleep in its own bed tonight,” he said, apparently happy to be home after a whirlwind tour of the Midwest.

But Mayer seemed to make a point of any overt references his romance with Aniston, saying more than once that the night would be about “more music” and “less talk.”

The rock life seems to appeal to Jennifer Aniston, as she continued to follow boyfriend John Mayer on his U.S. tour this past weekend. The latest stop on the Mayer-Aniston journey: Rothbury, Mich.

The star of the upcoming film Marley %26 Me watched Mayer’s set Sunday at the Rothbury Festival from off stage, while he crooned for 90 minutes.

The Detroit News reports that photographers used telephoto lenses to attempt to get a shot of Aniston.

Aniston doesn’t limit herself to domestic travel. Last month, she trekked overseas to London to see her man perform.

Jennifer Aniston and John Mayer continued to keep their romance firmly off the radar Saturday.

Slipping unnoticed into the musician’s backstage area at the Hard Rock Calling festival in London’s Hyde Park, Aniston stood quietly in the wings while the “Georgia Calling” singer ran through a 45-minute set in front of an audience of ten of thousands.

But the actress wasn’t just there to lend moral support: wearing a black-and-white floral halter-neck top and faded flared jeans, Aniston busily snapped away with her camera to record Mayer’s on-stage performance.

Earlier this week, the couple united in Amsterdam, where she was promoting the upcoming Marley and Me (with Owen Wilson) and Mayer was performing.

In keeping with the low-key theme of her London visit, she never once ventured into the Hard Rock VIP area and quietly left the show without anyone noticing.

Even the paparazzi camped outside her London hotel were left guessing.

Mayer later appeared on stage at the end of the show alongside headliner Eric Clapton and Aniston’s close friend Sheryl Crow. But again Aniston was absent.

Mayer is due to perform at the Glastonbury Festival on Sunday. His European tour then moves onto Copenhagen.

Jennifer Aniston made her first appearance at a gig on the European leg of boyfriend John Mayer’s tour Friday, and was there again Saturday at the Hard Rock Calling concert in London.

“She was on the side of the stage and really couldn’t be seen by anyone,” an onlooker tells PEOPLE. “John didn’t make any call-outs to her during the Hard Rock Calling show, but she was seen hanging out with him in the Artist Area before and after his performance.”

On Friday, Aniston arrived at side entrance of his show in gritty Brixton, south London, around 8.30 p.m., looking casual in dark blue jeans and stepping out of a red Range Rover.

At one point, he said, enigmatically, that “every relationship someone steps into might some how shake you up a bit. So I’m gonna take my time a little bit.”

Fans outside the gig said they had seen Aniston sitting in an upper level, playing with her hair watching the singer, and she and Mayer were seen leaving around 11:30.

Earlier this week, the couple had been united in Amsterdam, where she was promoting the upcoming Marley and Me (with Owen Wilson) and Mayer was performing.