Please be kind to yourself about any guilt that you feel. One thing a NPD does to us is to create tremendous amounts of guilt. There is earned and unearned guilt. It is very difficult for us to discern which is which. People who have dealt with NPDs' and survived understand this, and we are here to help you discern. The guilt comes and goes with me. I think I may be dealing with this for a very long time, but I work very hard to discern, and most often find that I am feeling UNEARNED guilt. None of us "don't understand" why you did what you did.
Ask yourself if your guilt is earned or unearned. 99.9% of the time, it will be unearned guilt that you were trained to feel.