The couple split in January but sparked rumours of a reunion when the 20-year-old actress flew out to Oslo, Norway, last week to see the singer, and friends says the brunette beauty initially dealt well with the split because she was busy promoting 'Spring Breakers' with Ashley Benson and Vanessa Hudgens.
A source told HollywoodLife.com: She didn't actually have to think of him cause she was with her girls doing major promotion.''
However, after the movie premiered last month, Selena had time to reconsider her feelings and reportedly realised she wanted to see the 'Beauty and a Beat' hitmaker again.
The source added: ''She was lonely. That is why she reached out to Justin again.''
Though Selena and Justin haven't confirmed whether they are back together again, the 19-year-old singer accidentally posted a photograph of the pair of them on his Instagram account over the weekend, but the image was quickly deleted.
And a source claimed to have seen the pair kissing in Oslo.
The source said: ''They were holding hands, hugging and they kissed on the lips. They looked really in love, like no fights ever happened before. It definitely looked like they were back together.''