The 40-year-old actor - who played teacher Will Schuester in the musical TV series - misses the late pair greatly and admits their deaths at relatively young ages are a stark warning about the pitfalls of the entertainment industry.
In an interview with Closer magazine, he said: ''Glee' was an amazing time. The cast all see each other now and then and keep in touch. I miss my friends, especially Cory and Mark. They were two incredible guys, they were on their own paths and what happened hasn't tainted the memories of 'Glee', but it's taught me about the business and the nature of fame.''
Cory - who played Finn Hudson in the Fox series - died in July 2013 at the age of 31 from an accidental drugs overdose.
Mark - who played Noah 'Puck' Puckerman - took his own life in January 2018 at the age of 35 as he awaited sentencing for the possession of child pornography.
Matthew - who will soon be judging new BBC talent show 'The Greatest Dancer' alongside Cheryl and Oti Mabuse - has remained friends with many of his former 'Glee' castmates and he admits it made him very happy when the show's co-creator Brad Falchuk married Gwyneth Paltrow, who played substitute teacher Holly Holliday in several episodes.
He said: ''Working with Gwyneth was amazing - I was always such a fan of hers, so working with her was incredible. She's such a close friend of mine, and it's awesome because she's now married to one of my great friends, Brad. They're both wonderful people.''
These albums are not nearly as appreciated as they should be.
Listen to her new song 'Callous Copper'.
They might sound like they're from the 70s, but they way they roll is very 2020.
'U Kin B the Sun' is an album rich in texture and depth and one that quite obviously, and unapologetically, plays to Frazey Ford's strengths.
Listen to their new single 'Small Change'.
Lissy Taylor's 'Mayday' might be born out of distress, despair and some despondency but it rails against the negativity of bad relationships.