I'm getting involved with the girlfriend of the guy who cuckolded my girlfriend... and I'm apparently getting satisfaction from it without even realizing it.

A protagonist whose girlfriend was taken from him has lost all motivation and now lives merely out of habit. However, it seems some of his softhearted nature remains—he still lends a hand when consulted or relied upon by others. One day, while reading a novel, he is suddenly spoken to. Then, everything from before comes rushing back like a tidal wave. Will he be able to remain alone until the very end? This is a story after such an NTR.