Jen and her new man Justin Theroux couldn’t be happier — but now her ex crooner is crawling back! Has this ever happened to you, HollywoodLifers?

Thank you John Mayer, because you’ve just proven my theory. I’ve always told my girlfriends that an ex-boyfriend is never really gone. They may dump you, cheat on you, call you names — but they always come back. Now that the gorgeous Jennifer Aniston is glowing with her beau Justin Theroux, it’s reportedly killing her ex-boyfriend John. But you know what I say? Serves him right!

Jen and John began dating in April of 2008 and they broke up 3 1/2 months later. But Jen finally dumped John for good in 2009.

“John always held out hope that he and Jen would get back together,” a source tells The National Enquirer. “When he found out she was hot and heavy with Justin, he flipped out.”

Too bad John.

I once had someone tell me this: “One day when you’re done trying and he’s done having fun, he’ll wake up and realize things could have been different. But it’s on that day that you’ll be waking up to the one that already knew.”

I want every girl that is out there sleeping on a tear-stained pillow to wipe their eyes and pull a Jen! Go out there and find that guy, call it a rebound if you want. But either way, you’ll find happiness and that man that broke your heart will come a knocking — trust me. But it’s at that moment that you won’t care anymore and you will have moved on to bigger and better things like Jen.

The satisfaction of that guy coming back will undoubtedly be bittersweet. But listen to me when I tell you this: happiness is the best revenge, especially when you’re not forcing it. Jen has finally found love and it’s John’s loss.

It’s guys like John that just don’t get it until it’s too late and you can only feel sorry for him. We told you Justin told Jen he loved her while Jen was cementing her hand and foot prints in front of Gauman’s Chinese Theater and she deserves it.

So ladies, if you’re worried that guy won’t realize what he’s lost — don’t. They always come back — just maybe not when you want them to.

— Chloe Melas