It is important to identify your part in it, how you allowed the abuse to occur. This does not mean beat yourself up over it; it means take a step back, asses the situation (now that you are out of it, it should be easier to do; you’ll have a clearer picture), and determine what role you played.
If you were the victim of an NPD parent, chances are you had no choice about being victimized, at least as a child. As you became a teenager, you may have still been a willing participant simply by not knowing any better, because NPDs destroy boundaries. Small children have no boundaries and are completely dependent on their caregivers; when those caregivers fail to teach the children to develop healthy boundaries, it will have a negative impact.
As you become an adult, you start to make active choices as to whether or not to continue enabling your NPD parent and allowing them to abuse you. You may even keep getting into abusive romantic relationships, because you believe that abusive behavior is normal. Or because the abuser took advantage of your vulnerability at a time when you were in just the right negative emotional state due to the loss of a loved one or some other devastating event.