His anger, fear, and self-loathing grow in a secret hidden part of himself and, since he hides this part of himself from himself, he is unable to recognize the source of these feelings. When they do surface, their source, to him, is his partner. This is projection.
Through this projection, he will accuse his partner of all that he does, and blame her for all the abuse that she suffers. She then becomes as he once was, wounded and without a witness to her wounding.