The Therapist Wants To Know

Oliver is a boy who's been held in his waiting room until he was called. Something came up with Oliver ever since Oliver was the first held hostage there and he wants to know what. Oliver refuses to tell what is wrong, he just uses key details. From what the therapist knows a male figure was abusive, he almost killed him, and Oliver had no choice but to stay with him. The question is... who is this?