You wrote:

she is the victim of my narcissistic behavior 

i’m feeling numb at this point. I don’t want to be an asshole anymore, but i can’t stop it

 I am feeling very ashamed of the things i have done, and i don’t know how to get over it.

What are you doing in addressing your narcissism?   You can Google how to cure or at least mitigate your underlying issues that drive your narcissism.

I believe that whatever shameful thing you have done and that she is holding over you cannot be worth the perpetual dysfunctional misery that you are constantly living day-by-day.

What is the cost of having your truth revealed?  I suspect it is not as costly as living the lie now.

Mark