In recent weeks, Justin has been hanging around with former child burglar turned rapper Sean Kingston, ex-convict Lil Wayne, and has collaborated on a new track with Chris Brown, who put his ex-girlfriend Rihanna in hospital after attacking her in 2009.
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However, the final straw allegedly came when Justin brought Sean to one of the19-year-old singer’s concerts in Florida last week.
A friend of Selena said: “Selena told him to stop hanging with these bad people. She didn't want him to crash her gig.
“They had a huge row and said it was good they were having time apart while she was on tour."
However, Justin is said to have taken the split badly, and was spotted in tears after one of their arguments.
The pal added to The Sun newspaper: “It's hard seeing a little 17-year-old crying and saying he loves her."