When news of Jennifer Aniston’s engagement broke late last week, all John Mayer could do was wistfully wonder what might have been. The singer, now in a fledgling relationship with Katy Perry, knew he’d lost a good thing when his bad-boy ways broke them up back in 2009.

"Jen really liked him," says a close friend. "He could've been where Justin is right now but he didn’t play his cards right. He regrets screwing up." The 34-year-old — nicknamed Mayer the Player — humiliated Jen by calling an impromptu press conference with the paparazzi after they split. "He played games," says the source. “Not calling her when he was on tour, coming up with all kinds of excuses not to show up to things...that sort of s**t doesn’t fly with adult women."

It’s this kind of behaviour that has Katy’s friends concerned for the pop star, 27, who’s fresh from her divorce from UK comedian Russell Brand. But a mutual friend of the hot new couple says John’s learned his lesson from losing Jen – and this time he’s playing for keeps.

"He’s very happy with Katy — and they’re much more of a good match," the source says. "They both have immature sides and serious sides, and they’re closer in age and career." And while John has — perhaps deservedly — beaten himself up over his Lothario ways, which also broke the hearts of Jessica Simpson and Jennifer Love Hewitt, a close insider says he’s ready to move on from that time in his life.

Read more about John and Katy in this week's Woman’s Day on sale Monday August 20, 2012.