In the September issue of Cosmopolitan, Lovato, 22, reveals the only time she and her love of five years broke up was when she was relapsing.
"People say that relapses happen before you use. Your mind starts setting up the relapse before you take that drink or that first hit," she says. "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."
The couple started dating when Lovato turned 18, "right after" she entered rehab for emotional and physical issues.
"People told him, 'You should probably leave. She's on a spiral, and you're going to be sucked down with it,'" she says of Valderrama, 35. "But he was like, 'I'm not leaving. This is somebody I really care about,'" says the "Cool for the Summer" singer.
The entertainers "relate on a lot of levels," adds the star. "I've seen a lot of s---. S--- people don't know about. He's seen a lot of stuff too."
Lovato recently worked with her boyfriend on Valderrama's vampire show From Dusk Till Dawn: The Series.
"My love… Always supporting me on set… At 4 a.m. even if he has to get up to work at 9.." she captioned a cuddly photo of the two on her Instagram.
One thing Valderrama is not? Jealous – even when it comes to her exes.
"Nick [Jonas] and Wilmer get along great – Joe and Wilmer too. It's weird. In the beginning, I was like, 'Why the f--- are you friends with Joe?' He was like, 'He's a cool guy.' Yeah, I know. I dated him."
TESH / Cosmopolitan