Boku ga Suki da to Ienai Wake
僕が好きだと言えないワケ · ぼく が すきだ と いえない わけ
est. Rough estimate based on volume count, reprints and magazine — not an official figure
Overview
After divorcing his wife, Tooru was all alone. The only one he'd been relying on was his (now ex-)wife's nephew, Masachika. With his connection to Masachika now lost, Tooru's loneliness grew until one day...?!
Source: AniList
External databases: MADB · AniList
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections