Sharing a sweet picture that shows her resting her head on Cory's shoulder, Lea wrote: "We hold you in our hearts today, and every day we remember your smile. We will love you and miss you always."
The actress, who met Cory on the set of Glee, posted a second picture on her Instagram page of the couple standing on a beach and smiling, with their arms wrapped around each other.
Lea Michele shared this photo as she marked the anniversary of Cory Monteith's death
Also remembering Cory on Sunday was his Glee co-star Matthew Morrison. "I personally believe Cory was reborn into some other beautiful form a year ago today," he wrote on Twitter. "I celebrate him and his life… Wherever that may be. Happy birthday my friend… I miss you."
Glee creator Ryan Murphy, meanwhile, shared a screenshot from the late actor's special tribute episode, The Quarterback, simply writing, "Miss you".
"I still miss him very much and I still have that empty feeling," Joe told ET Canada. "Cory was a likeable young man and if he was in the room, you'd be smiling. He enjoyed life. That's why I was so shocked about the outcome of events."
Speaking about Cory's then-girlfriend Lea, Joe added: "She's a beautiful young woman. She should enjoy life. She had a good time when she was with Cory, from what I understand, but life's gotta go on."
Lea Michele recently started a new relationship with Matthew Paetz
Just recently, Lea has felt ready to do just that. She has found love with Matthew Paetz, an aspiring actor and model who appeared in the music video for her single, On My Way.
It is the star's first romance since Cory's death. "I feel like it's so important to make sure that I'm 100 per cent ok before I can get into a relationship," Lea told Glamour magazine back in February.
"But people have to understand that I can't be alone forever. Cory wouldn't want that."