After all, during Bieber's recent arrest for a DUI and subsequent scuffles with the law, Gomez kept both her distance and silence, even checking into a rehab facility "to clear her mind" for two weeks in January, according to a source close to the pop star.
"She felt very empowered after that," the source tells PEOPLE. "She did well for a few months. But then she hung out with him again."
So what exactly is it about Bieber, 20, that keeps Gomez, 21, coming back for more?
"He's very charming," says an industry insider. "I'm not sure what's going on with him right now, but he's very smart, and used to be a very fun and funny kid."
He also apparently knows how to get inside Gomez's head.
"Whenever they're not talking, he has to do something to get her attention, like posting [a photo of her at the Vanity Fair Oscars party], captioned 'most elegant princess,' " the source says. "He reaches out, then says he's going to come see her and she's like, 'Okay.' It's a pattern on his part. The sad part is, she always goes back to him."
It's not the first time this has happened. Days after the couple announced they were breaking up in Nov. 2012, Bieber was seen picking Gomez up from the airport. At her birthday party in July, he showed up uninvited with a rose, and she later left with him. And in January, the two were seen riding Segways around his Calabasas, Calif., neighborhood, before he posted a photo of them cuddling on Instagram captioned, "Love the way you look at me."
This on-again, off-again pattern hasn't been sitting so well with Gomez's friends and family, who, after dealing with it for a year and a half, are sick of the drama.
"I believe Taylor's gotten fed up with it," the first source says of Gomez's pal Taylor Swift, who famously rolled her eyes at the two of them kissing hello at the 2013 Billboard Awards. "[Swift and Gomez] still talk, but she doesn't want to hear about it anymore."
Not even Gomez's family seems able to convince her to give him up for good.
"They feel like they've done all they could for her, and there's nothing else to do," the source adds. "At this point, she has to figure it out on her own."
For more on Justin and Selena, pick up the new issue of PEOPLE, on newsstands Friday.