When there is inconsistency in belief and action (such as being violated by someone who is supposed to love you) our mind has to make an adjustment so that thought and action are aligned. So sometimes the adjustment that the mind makes is for the victim to bring her or his behavior in line with the violator, since the violator cannot be controlled by the victim. Our greatest source of survival is to adapt to our environment. So increasing emotional intimacy with a person who is forcing physical intimacy makes sense in our minds. It resolves cognitive dissonance.
In 1973, Jan Erik Olsson walked into a small bank in Stockholm, Sweden, brandishing a gun, wounding a police officer, and taking three women and one man hostage. During negotiations, Olsson demanded money, a getaway vehicle, and that his friend Clark Olofsson, a man with a long criminal history, be brought to the bank. The police allowed Olofsson to join his friend and together they held the four hostages captive in a bank vault for six days. During their captivity, the hostages at times were attached to snare traps around their necks, likely to kill them in the event that the police attempted to storm the bank. The hostages grew increasingly afraid and hostile toward the authorities trying to win their release and even actively resisted various rescue attempts. Afterward they refused to testify against their captors, and several continued to stay in contact with the hostage takers, who were sent to prison. Their resistance to outside help and their loyalty toward their captors was puzzling, and psychologists began to study the phenomenon in this and other hostage situations. The expression of positive feelings toward the captor and negative feelings toward those on the outside trying to win their release became known as Stockholm syndrome.