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On being "off and on" for five years with boyfriend Wilmer Valderrama: "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."

On Wilmer not throwing in the towel: "We started dating when I turned 18 … Right after that, I went to rehab. People told him, 'You should probably leave. She's on a spiral, and you're going to be sucked down with it.' But he was like, 'I'm not leaving. This is somebody I really care about.' We relate on a lot of levels. I've seen a lot of shit. Shit people don't know about. He's seen a lot of stuff too."

On Wilmer not being the jealous type: "Nick and Wilmer get along great — Joe and Wilmer too. It's weird. In the beginning, I was like, 'Why the fuck are you friends with Joe?' He was like, 'He's a cool guy.' Yeah, I know. I dated him."

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On her music: "There are a lot of girls in pop. They have badass lyrics, but I feel like I'm the only person other than Rihanna and Nicki Minaj who isn't afraid to say, 'Try something on me and I'll fucking beat your ass.' There are people who can dress up and play the part, but their music doesn't say it."

For more of Demi Lovato's exclusive interview and photo shoot with Cosmopolitan, pick up the September 2015 issue on newsstands August 11 or click here to subscribe to the digital edition!