Ore no Kanojo to Osananajimi ga Shuraba Sugiru
Source
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Eita enters high school aiming for the National University School of Medicine. Because of his parents' divorce—and his goal—he shuns anything to do with romance or love. One day, Masuzu, the school beauty with the silver hair who's just returned to the country, enters his life in a most unexpected way. Chiwa, his childhood friend since elementary school, will not let this go without a fight. *Note: Includes volume 6.5.*
Source
Eita enters high school aiming for the National University School of Medicine. Because of his parents' divorce--and his goal--he shuns anything to do with romance or love. One day Masuzu, the school beauty with the silver hair, who's just returned to the country, enters his life in a most unexpected way. Chiwa, his childhood friend since elementary school, will not let this go without a fight.
Sequel
An anthology of Ore no Kanojo to Osananajimi ga Shuraba sugiru by various mangaka.
Alternative
The story sets one month Eita and Masuzu start dating, and sets itself on a "what if" where the Harem element is stronger than in the original.