It's bad to not be understanding of your partner's past.
John asks Mary to marry him but before accepting she tells him she has a secret she has been keeping from him.
John wants to respond to Mary's revelation.
John decides to trust what he knows of Mary and encourages her to be open with him.
John gets angry that she has kept something from him and withdraws his proposal.
Mary is able to be honest with John and thus strengthen their bond.
Mary is hurt by his reaction and withdraws from him.