The 22-year-old model, who has been dating the designer sporadically for several years, was admitted to a treatment facility in Arizona in April (12) after he was arrested and charged with drug possession following a bust-up with a friend at his New York apartment.
Gruber has now announced he is out of rehab and is determined to make positive changes in his life.
In a post on his Facebook.com page, he writes, "Hey everyone. I just had such (an) amazing learning experience from rehab. I have learned so (much) about myself. I am so thankful that I went. I am a different person. I don't want to go back to my old self. I want to focus on my future on become (sic) a successful person on (sic) education, work and bettering myself everyday...
"No more partying. Time to be a grown adult. Thanks to rehab and the people who love and care about me. I am now going to aftercare. I want to better myself even more."
Gruber also reveals he is currently taking time out to enjoy a road trip across California.