The 32-year-old posted a photo of the sun showing through clouds over calm waters on Twitter, captioning it, “The light always remains,” along with the red heart.
Monteith, who played Finn Hudson on Glee, died at age 31 in a Vancouver hotel room of an accidental mixed drug toxicity in July 2013.
The pair, who met on the set of the hit show in 2009, dated from 2012 until his death.
In 2014, Michele spoke to Seventeen magazine about their romance, saying she only had “happy memories” of the actor.
“He was not his addiction — unfortunately it won,” she said. “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.”
Michele, who portrayed Rachel Berry on the show, was not the only Glee alum to pay tribute to Monteith; Kevin McHale, who played Artie Abrams, shared a photo of his friend on Instagram and captioned it, “The sweetest boy. Forever,” along with six black hearts.
Heather Morris, who played Brittany Pierce — and attended Monster Jam with costar Naya Rivera on Saturday — commented on the post, writing, “Missing him a lot lately.” Meanwhile, Matthew Morrison (Will Schuester) wrote, “Ha! I love this pic!”