Valderrama marked the milestone on Sunday (15Mar15) with a touching tribute to the Skyscraper hitmaker, three years after she addressed her eating disorder and drink and drug issues in rehab.

He wrote, "Today, we lay another stone together. It is now 3 years since you said: I am more important then any past, demon, disorder or addiction. Where you decided that YOUR life was worth living while loving yourself. And I'm sure glad you did.

"I knew then the woman you've become now. I am proud and honor (sic) to be front row to see the world you are about to change. I love you Demi."

Now Lovato has returned the kind words in a post on her own page on Monday (16Mar15).

Alongside a black-and-white photo of the couple sharing a kiss, she writes, "I wish I could put into words how grateful I am for this man right here. 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 making 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. I really wouldn't be alive today without him. I love you Wilmer."

Lovato's public declaration of love comes over three months after she revealed Valderrama helped her stay healthy after she almost suffered a setback in her eating disorder battle in 2013.

The star has also taken to her page to thank fans for their support, writing, "I'm still catching up to texts and congrats tweets... Thank everyone who has supported my journey. I never knew sobriety was possible for me But with the love and support I've been given from my friends, fans, and family.. I now celebrate my 3rd birthday. Thank you to everyone".