Tell your friends and family they can't trust the key anymore
Discussion
Just publish the nsec for everyone to see. There's no more effective way of repudiation.
But what about my private messages
I don't know what private messaging you use but if it doesn't offer PFS you're screwed.
I use this https://github.com/nostr-protocol/nips/blob/master/04.md is it not private and secure?????? What does PFS do????? I
Mebbe it's one of these https://acronyms.thefreedictionary.com/PFS