https://www.mangago.me/read-manga/faded_first_love/
One of my favourites ^^
technically yes? since the very minor side couple is the ml’s own younger sister and her new second time around husband but besides being mentioned and making a few appearances every now (story itself is still ongoing) and then they don’t really take over the story much thankfully
https://www.mangago.me/read-manga/yatara_yarashii_fukami_kun/

Has anyone ever found a bl with a straight side couple? I was reading one with a lot of gay side couples and started wondering if there's any with a straight side couple.