The pair had a secret meeting in Atlanta in November and were spotted kissing in September, and both girls now think they are the teen heartthrob's girlfriend.
An insider told The Sun newspaper: "Justin and Jasmine have been closer than they have let on for some time.
"He turned up on her video shoot and they were kissing and cuddling. She refers to him as her boyfriend. She also went to Atlanta to visit him.
"But Selena seems to think she's his girlfriend too. She's been gushing about him to her friends - and they had this cute breakfast date in Philadelphia this week.
"Justin could take his pick of the world's teenage girls - and he's loving it. Two older women on the go aged 16 is pretty impressive stuff."
Earlier this week 'Magic' singer Selena revealed she "loved" Justin.
Discussing her closeness with him, she said: "I love him, he's one of my best friends. I would do anything for that kid."