It's fucking incredible if Rei never told the fact of he fuck with other woman apart of Nagi, maybe he and Chako fucks. But he doesn't because Chako is special for him.
Between Chako being a manipulator, his teacher being a nut and his mom....well, whatever, I understand now why Rei will go back to Nagi to end it. He has no one in his life who gives a damn about him truly.
Just when you think the story couldn't get any more depressing, it just keeps spiraling farther and farther down. It's sad to think that the things and feelings the characters are having exist in real life...