It's petty to leave someone because of trivial transgressions.
Frank and Nancy have been dating for years but Frank is upset that Nancy called him at work.
Frank wants a happy relatioinship.
Frank reminds Nancy he can't talk at work and tells her he's looking forward to dinner with her.
Frank tells Nancy it's not working out and leaves her for another woman.
Nancy respects Frank and loves him and Frank enjoys his relationship.
Nancy is very sad and Frank finds out later that no relationship is perfect.