Initially they were the best of friends, but Josie wanted to be with John Barton because she thought he was the best man she would ever meet. She sees him as an upper class man who is witty, charming and everything she wants in a man. John Barton also likes her and doesn't feel any racism towards Josie at all, but he has mixed feelings between Josie and Ivy. Josie wants to be in the same law class as John but he isn't allowed to choose what course he wants to study in because he is under constant pressure to do what his dad wants him to do.
As the book progresses John Barton and Josie become closer together because John was spending more time with Josie than with Ivy, so Josie believes that John is falling for a middle class working woman over a upper class snob like Ivy. Josie also sees a side of John she doesn't like, he was extremely negative about life which Josie disagreed with and didn't like what he was saying so they start to break away a bit at that moment because of his negativity towards life.
Josie and John grew even closer when they wrote down their deepest feelings and gave it to each other to hold onto, which before then she was too afraid to tell anyone what she was thinking, which by this action of trust was a definite big step towards their relationship. John wanted to go against his father's wishes and take control of his own life and enrole in the law course. A couple days after John decided what he wanted to do in life he committed suicide, most likely because his dad disagreed with his actions that caused him into a depression. John never tried to get into a serious relationship with Josie or Ivy because he new the only way he could be free was to kill