Kimi to Tokei Series

Soushi Kijou is a 17-year-old high schooler. Five years ago, Seria Orihara, his childhood friend and first love, cut off relations with him because of a "certain lie". One morning, he awakens from a nightmare in which Seria dies. The nightmare leaves him with an uncomfortable feeling, which sticks with him until he goes to school and enters the classroom... Upon which he discovers that his one-and-only close friend Kazuki Kaidou is being erased from existence. Soushi is the only one to realize this, but picking up on his strange phenomenon, an older girl named Chitose Kusanagi and an unusual classmate named Hinami Suzuka form the "Clock Club" with him in order to find the truth behind the distortions in the space-time continuum. Can these three solve the time travel-related mysteries that are taking place in the world?!

(Source: Kodansha, translated)