Turning away can be just as painful. What if you could help that person and you didn't care enough to?
As for leaving, what about the fear, despair, and isolation that abused people feel? They may leave, but abuse can form a dependence because the person being abused feels that they are not good enough to be treated better or to be loved. Someone may be able to leave, but that doesn't mean there aren't consequences for the actions that people take. Even at gunpoint, the abused is still free to leave. People of all genders, age, culture, creed, religion, etc can suffer from abuse; also, abuse does not have to be only between two people (such as a man and a woman). The jewish people were abused brutally by the Nazis in death camps. There are plenty of examples in history of abuse, and I don't think that we should hold those abused in lower esteem or just stop caring. Elie Wiesel (a holocaust survivor) talked about the dangers of apathy in some of his speeches. We can be as much of the cycle of abuse by not helping someone in need.