When, where, how?

We are engaged, live together, have joint finances and everything. I've been thinking of a breakup for a really long time, just wasn't sure if I should do it.

How do I approach the topic, do I pack his stuff, help him pack? Do I tell him why? I have to be prepared for everything.

It might come as a total surprise for him.

I have valid reasons for leaving, he wouldn't understand. He is severely narcissistic (npd).