Lovato, 22, snapped a kiss with Wilmer Valderrama and posted the black-and-white photo along with a personal message.
“I wish I could put into words how grateful I am for this man right here,” she wrote. “But my love has grown to a level that words could never possibly express how much this man completes me. He’s loved me the way I never thought I deserved to be loved and with this day marking my 3rd year sober After sharing my ups, putting up with my downs and supporting my recovery he still never takes credit and I want the world to know how incredible his soul is.”
She concluded with, “I really wouldn’t be alive today without him. I love you Wilmer.”
On Twitter, Lovato also thanked her friends, fans, family and everyone else who has supported her the past three years.
The singer, who has struggled with eating disorders in the past, often posts photos promoting a healthy lifestyle. Her most recent was a photo of herself and Valderrama working out together and a solo sunbathing shot.
Wrote Lovato in that caption: “Regardless of what society tells you these days … You don’t have to have a thigh gap to be beautiful. It is possible to love your body the way it is.”