If your neighbor stole your car, you would report him to the police. Your abuser stole something from you much more valuable than a car. He stole a part of your very life and self from you. In doing so that person committed a crime and needs to suffer the consequences of his or her actions. It is not unforgiving or unchristian to report such a person. In fact, it is wise to do so. It forces the person to deal with the reality of what he or she did. It also reduces the likelihood that the person will abuse others in the future.
God established the church to help us forgive. He established the government to provide temporal justice and curb lawlessness in society. As Christians we enjoy the benefit of both realms.