https://www.mangago.zone/read-manga/someone_else_s_bl_manhwa/
https://www.mangago.zone/read-manga/that_summer_kim_hyun/
these are more "they lowkey like each other from the start and are using the love triangle to make each other jealous" but this is as close as I could get sorry. ╮( ̄▽ ̄)╭
hours after I replied i saw this comic in my feed, it is exactly what you described, however the person at the center of the harem ships the two guys who like him, so it's not exactly a love triangle. ╮( ̄▽ ̄)╭
https://www.mangago.zone/read-manga/nande_koigataki_ga_ki_ni_nannen/
does anyone know a manga/manhwa wherein two male leads likes the same person but they end up together instead?