A discreditable lack of gratitude.

Someone who used to be a potential girlfriend/boyfriend, but no longer is.

Ingratitude is thinking nothing of what has been done or given to you by someone else. That is to say, not feeling bound to show gratitude. In other words, ingratitude is a discreditable lack of gratitude. In fact, it is simply lack of appreciations or thanks for something given or done to you or to someone else. -Emeasoba George

A discreditable lack of gratitude.