The 21-year-old singer had sparked reconciliation rumours in January after she was spotted holidaying with Bieber, reported Hollywood Life.
"Selena is sad but she's also angry. She feels like Justin played her because just when she was getting some closure and strength he convinced her to come back to him and made all kinds of promises. But it turns out they were all lies and now she's back at square one," a source said.
"In a way she's mourning because she's realised that he just isn't the guy she fell in love with anymore," the source added.
The teen heartthrob has been in news for his wild antics that include throwing eggs at his neighbour's door, spitting at fans from his hotel balcony, getting his home raided by police and frequenting stripping clubs.