The 23-year-old Australian singer voiced his love for Cyrus, 27, Tuesday on Instagram Stories on their six-month anniversary as a couple.
Simpson shared a black and white photo of Cyrus smiling while sitting at a table.
"6 months with you is worth a lifetime with anybody else," he captioned the post. "I love you."
Simpson released his third studio album, Free, in 2015, and the EP B-Sides: Part the Seas in 2019. He is known for the singles "iYiYi" featuring Flo Rida, "On My Mind," "With U Were Here" featuring Becky G and "Flower."
In addition, Simpson will release his debut poetry collection, Prince Neptune: Poetry and Prose, on April 7. Simpson will promote the book with a live performance and reading April 7 at 3 p.m. ET on Instagram Live.
Cyrus came to fame on the Disney Channel series Hannah Montana and released her sixth studio album, Younger Now, in 2017. She has been creating the Instagram Live series Bright Minded: Live with Miley during the coronavirus outbreak, and recently spoke to Paris Hilton about female pop stars and ignoring online haters.