How to break up with NPD?

How to break up from a relationship with a man diagnosed with Narcissistic Personality Disorder? You have been together for 4 years, your entire lives are intertwined and he has things he can use against you to ruin your life?

It has to be calm, and I have to be smart about it. For obvious reasons I can't simply be honest with him and truthfull bacause he has a complete lack of empathy and he will use everything against me in arguments (manipulative, has to be in the right etc).

He has been abusive and I can't use that against him (in terms of reason for breakup) as he does not understand the concept of a victim (he is always the victim).

Any serious comment might just change my life for the better ❤