As Cory Monteith's friends and family members struggle to come to terms with the Glee actor's untimely death, it's clear that his influence was far-reaching — and that he kept his private struggles close to the vest. As his ex-girlfriend, Mallory Matoush, tells Us, Monteith was "just a happy guy."

In fact, Matoush tells Us, she never saw any signs of problems when they were together. "Cory kept me in the dark about his drug use," she exclusively tells Us. "He told me about his teenage days and his past problems but he never used anything in front of me, ever."

During their months-long relationship, Matoush says, she only saw the actor drink, but never to excess. "He was always so silly and funny," she remembers.

"My favorite memory is when Cory was in town for Jimmy Fallon," the New Yorker says. "We went for dinner after. He was still wearing what he wore for the interview. He was sitting on the couch in his hotel room the same way he sat on the show."

"I pointed it out and he was laughing hysterically for like 5 minutes," she continued. "He would always make a joke about everything and was just a silly guy."

Monteith and Matoush initially met in June 2011 and the pair hit it off right off the bat. Though they only dated for about eight or nine months, Matoush says, they ended their relationship cordially and remained on good terms.

"Cory was so normal. I didn't even know who he was when I met him," she remembers. (Monteith would later begin dating Glee costar Lea Michele; the couple made their red carpet debut at the People's Choice Awards in January 2012.) "I had to Google it because after the first night I stayed with him, I was on my way out of his hotel and there was a crowd of young girls waiting for him. They asked me if I had seen Cory Monteith inside the hotel and I was so confused."

The Glee star was found dead in a hotel room at the Fairmont Pacific Rim Hotel in Vancouver, Canada, on Saturday, July 13. He was 31 years old. An autopsy of the late actor's body will be conducted on Tuesday, July 16, the British Columbia Coroners Services tells the Associated Press.

Earlier this year, Monteith had checked himself into rehab after admitting that he'd relapsed in his battle with addiction (a problem that began at age 13), and appeared to be fine upon leaving the center on Apr. 26.

"Sending out big love to everyone," he tweeted to his fans at the time. "Thank you for the continued support! It means the world to me!"

Matoush, who found out about the devastating news while she was at work on Saturday night, says she is in "complete shock" over his death.

"He had so much more to do," she adds. "He would have done such good things with his life. He was such a talented actor and an even better person. I will miss him."