Demi Lovato can't understand why boyfriend is pals with her ex

Pop star Demi Lovato is puzzled about her boyfriend's friendship with her ex, Joe Jonas.

The singer has challenged Wilmer Valderrama over his close ties to the former Jonas Brothers star, admitting the relationship is "weird".

She tells the new issue of Cosmopolitan magazine, "In the beginning, I was like, 'Why the f**k are you friends with Joe?' He was like, 'He's a cool guy'. 'Yeah, I know. I dated him'."

Lovato tells the publication she and Valderrama have been an item for five years, adding, "The only times we ever broke up were when I was relapsing, whether it was drugs or in a bad place and rebelling against everybody, not just him...

"People say that relapses happen before you use. Your mind starts setting up the relapse before you take that drink or that first hit. The times we'd broken up, I had already gone to that place of, 'Yeah, this is what's happening'. I didn't realize it at the time, but I just wanted to sabotage everything around me so that I could sabotage myself."

Lovato spent a lengthy period in rehab in 2010 and 2011 addressing her self and substance abuse issues, and often credits Valderrama for her ongoing sobriety, admitting he has been there for her at her lowest moments.

Ironically, she was on tour with her ex-boyfriend Jonas' band in South America when she suffered a meltdown backstage. The incident sparked her rehab stint.