Lea Michele & Cory Monteith

The 'Glee' star's boyfriend of 14 months and co-star was found dead in his hotel room in Vancouver, Canada, on July 13 due to an overdose from heroin and alcohol, and despite bravely returning to the set of the FOX series this week, Lea is struggling to get out of bed every morning.

A source close to the brunette beauty told People.com: "Every day is so hard. Just getting up in the morning means remembering that Cory is gone. It's incredibly painful.

"It's a struggle. She is incredibly strong, but that doesn't make it easier."

The actress is expected to make her first red carpet appearance since Cory's sudden death at the Teen Choice Awards in Los Angeles, on Sunday, which will include a special tribute to the 31-year-old actor.

Earlier this week, Lea said it felt good to be back at work on the set of 'Glee' so soon after her boyfriend's death.

She posted a picture of herself in character, Rachel Berry, sitting on the bed, gazing at the floor, with the caption: "Feels so good to be home..."

She also wrote: "First day of glee today. And at my first wardrobe fitting for Rachel Berry for Season Five! I've missed her so much (Sic)."

'Glee' bosses will film a memorial episode for Cory - who portrayed Finn Hudson - which will reference the dangers of substance misuse.