The 22-year-old singer marked the milestone by sharing a photo of herself with boyfriend Wilmer Valderrama and captioning the picture with a sweet message to the 35-year-old actor.
"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..."
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