Details regarding Cory Monteith’s decent into drug addiction may help people understand the late star’s downfall. The 31-year-old battled substance abuse since he was 12-years-old and dropped out of school at age 16. The “Glee” star was able to get and stay clean for a while, but his sobriety was short lived. Check out the vid to see exactly what went wrong after Monteith’s stint in rehab and be sure to watch "omg! Insider" for the latest in entertainment news.