But his acting coach and friend Andrew McIlroy tells PEOPLE that the three pals who the 31-year-old spent time with on the evening of July 12 – before returning to his hotel room by himself in the early morning hours – were positive influences in the Glee star's life.
"They weren't strangers, they weren't bad guys. They were longtime sober friends. Cory knew them maybe 10 years. Essentially, he had spent time with [them] as sober people," McIlroy tells PEOPLE. "They were not using with him [that night]. There was no double life up here."
The last time McIlroy saw Monteith was a few weeks before he passed. "He was just recently out of rehab and he was good," he says. "He was happy to be breathing fresh air and putting in full days and being active."
Monteith was scheduled to have breakfast with McIlroy the morning he passed away. "He was fine, that's what's so awful," says McIlroy of how the three friends described Monteith's demeanor during their outing the night before. "The vigilance against using is nuts. If I or anyone understood the mindset nobody would ever slip."
Fans of Monteith may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.