I may sound crazy for saying this but i think the "cure" for all of this is the most least expected character in this story, Yuko herself. I also believe she will be the one to save Nagi from the teacher and Reiji as well. After Nagi last gesture of kindness by returning her first love back to her, she will be rekindled and finally ''approve'' her in a way like what she did to her in the hospital. She know Reiji is a good boy deep inside and so the only for her to save him to free him, complete freedom from her terrible past. This may sound cliche but I think this will be the best ending. As she does all of that, the manga will end where weeks past and she finally pass away.