"4 years and it still feels like yesterday.. love you more," she wrote in Thursday's message, which accompanied an image of her with her eyes closed and her cheek pressed against Monteith's smiling face.
Monteith was a singer and actor best known for co-starring with Michele on the hit TV series Glee 2009-13. He was 31 when he died of a toxic combination of heroin and alcohol in a Vancouver hotel room on July 13, 2013, after years of battling substance abuse addiction.
Michele's songs, "Hey You" and "If You Say So," are about Monteith.
Glee alum Kevin McHale also paid tribute to Monteith this week by sharing a photo of himself with the actor and several of their other castmates.
"Sometimes it feels like you'll just walk on through that door with that voice and that grin. Miss you every damn day," McHale said.