Boku no Kirai na Otouto

Shiina and Kazuya become brothers when their parents decide to marry. With a 5 year difference, Kazuya who works as a chef takes care of his new younger brother who cannot eat strangers' food, apart from Shiina's. 3 years later, Kazuya seems to have grown more unsociable with bouts of jealousy over his brother to the point of sexually assaulting him. Shiina is lost as he does not understand what has changed and what he can do to fix things, while running away is not working out. Can the 2 brothers finally communicate their feelings and bridge the gap? Note: Includes 1 extra chapter.