It's back on for Selena Gomez and Justin Bieber's rollercoaster relationship — and this time, it's serious.

So serious, in fact, that the couple — who reconnected over the phone while Sel was in rehab — are planning to get married in the near future!

A source exclusively tells In Touch that Selena was very open to bringing her former flame back into her life, but under one condition … that he proposes!

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MORE: Did Selena Gomez Accuse Justin Bieber of Cheating? Find Out!

"She's already talking as if they're engaged," the source adds.

For more on Justin and Selena's wedding plans, pick up the new issue of In Touch, on newsstands now — and click through below for more adorable pics of the couple!