KEKKON NO KATACHI: SWAP KON

Two couples living in a certain apartment building, rumored to be the "ideal couples," have a secret. It's a swap marriage—a fake marriage between two same-sex couples. A "lavender marriage" allowing you to live freely with the person you love, should have nothing but advantages, but...!? (Source: Shueisha, translated) — Description from AniList community (anilist.co).