#035 of Atomic Bunko/Atomic Pocketnovels, the first volume of the story. This book might be influenced by 俺の彼女と幼なじみが修羅場すぎる (abbr. Ore-Shura), or, at least the title is. An interesting story to read.
info on mugi: http://doujinshi.mugimugi.org/book/563087/