Justin Bieber's 'soulmate' Selena Gomez

Justin Bieber thinks Selena Gomez is his ''soulmate''.

The 21-year-old singer - who was in an on/off relationship with the actress from December 2010 until last year - reportedly thinks the pair are perfect for one another and ''hates'' being apart from her.

An insider said: ''For him, they weren't just in love, they were soulmates, and he hates when he can't have her in his life.''

The 'Boyfriend' hitmaker has been spotted spending time with model Hailey Baldwin and reality TV star Kendall Jenner in recent months, sparking rumours of flings with both girls.

However, the source insists Selena is still the apple of Justin's eye.

They told HollywoodLife.com: ''Despite things with Kendall Jenner and Hailey Baldwin, Justin has always held a torch for Selena.''

Meanwhile, friends of the 'Come & Get It' hitmaker are said to be becoming increasingly worried that the 22-year-old star will fall back into ''old bad habits'' with her former beau since her close pal Taylor Swift has found love with DJ Calvin Harris.

It has been claimed Selena has been feeling left out since Taylor, 25, got together with the 'Summer' hitmaker and is considering reuniting with Justin.

A source said: ''Taylor is totally consumed with Calvin right now and barely has time for Selena. Taylor was always on Selena about staying busy and staying away from Justin.

''Selena's friends still wonder why she's so caught up in what Justin is doing. They worry that she's falling back into her old bad habit of obsessing over what Justin is doing and saying. It's like she's still invested in the relationship even though it ended months ago.''