As such, they unwittingly place themselves in a position to be taken advantage of. The more approval is needed, the less likely is the individual to realize the extent of their self-sacrifice in favor of tending to the needs of the other. Targeting the appropriate person may jeopardize a source of approval and self-esteem. To avoid facing reality, they distort it. They justify the other person's behavior by thinking they must deserve the treatment they are getting.
Anger is healthy.
It is a signal that something is wrong and needs attention. Codependent people are expert at denying anger and turning it against the self - into sadness and depression. Unarticulated anger is often misdirected and expressed inappropriately. The cognitive and verbal skills to appropriately assert oneself are lacking. If they really loved me, they would know.