Selena Gomez reportedly can't resist Justin Bieber because he is ''very charming''.

The 'Come & Get It' hitmaker, 21, felt ''very empowered'' after checking into a rehab facility for two weeks in January to ''clear her mind,'' but friends aren't surprised she has reunited with her on/off boyfriend because he always knows how to win her back.

A source told People magazine: ''He's very charming. 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.

''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.' 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.''

Justin, 20, who has been dating Selena on and off since 2010, also dedicated a song to the brunette beauty during a surprise performance in Texas earlier this month.

He turned up at the Banger's Sausage House and Beer Garden in Austin for the South by Southwest festival and sang his hit 'As Long As You Love Me' for his ''baby'', who was standing in the wings.

But Selena's friends, including her best pal Taylor Swift, are sick of the drama and want her to end her relationship with Justin for good.

The insider said: ''I believe Taylor's gotten fed up with it. [Swift and Gomez] still talk, but she doesn't want to hear about it anymore.''

Selena's family also want her to move on but don't know how to help her.

The source said: ''They feel like they've done all they could for her, and there's nothing else to do. At this point, she has to figure it out on her own.''