君と一緒にいたのに、一人のときより淋しかった = Though I was with you,I was more lonely than when I was alone.
きみ と いっしょ に いた のに ひとり の とき より さみしかった
est. Rough estimate based on volume count, reprints and magazine — not an official figure
External databases: MADB
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections