The metaphysics of betrayal

Why would someone betray? I am talking about an every day, little detail, an almost unnoticeable betrayals. For example, throwing a tandrum and playing a power game when a loved one needs something direly. Putting the loved one in need, in a predicament where he or she has to give up their pride to obtain cooperation. Why do people do that? What drives them, from the philosophical point of view? How can such a conduct be justified to their own selves?