Monteith would have turned 32 on Sunday.
"The biggest heart and most beautiful smile," Michele wrote. "In all of our hearts.. We love you so. Happy Birthday."
She also shared a sweet photo of herself laughing with the late Glee star.
The biggest heart and most beautiful smile.. In all of our hearts.. We love you so. Happy Birthday. pic.twitter.com/XzGVu0g5nY— Lea Michele (@msleamichele) May 11, 2014
"I only have happy memories of Cory," she said.
"He was not his addiction -- unfortunately, it won. But that wasn't who he was. Cory made me feel like a queen every day. From the minute he said, 'I'm your boyfriend,' I loved every day, and I thank him for being the best boyfriend and making me feel so beautiful."