That is not your problem.
Narcissists usually land on their feet. Boot him out and stop allowing him to manipulate you by making you feel sorry for him.
Kick him out. He's an adult --- he's USING your feeling sorry for him.
A - How do you know they are narcissist? B - Why do you assume that the friend doesn't already know? C - Why do you think they might want to know? D - Is it any of your concern? If you can satisfactorily (and honestly) answer those questions then yes, tell the friend, otherwise leave the matter lie.
I would.
Tell him to go and leave you alone.
On the contrary, most families leave the narcissist.
If a friend were in your situation, what would you advise?
I suppose. Absolutely
Leave, then empty the bank.
YES. IMMEDIATELY. IT WILL ONLY GET WORSE.
leave and/or abuse you and blame you.
Honestly... If this person won't leave their partner, then that means that they are happy. You can't force someone to leave their partner because YOU love them. Either hope and pray that eventually they do leave their partner, or try and find someone new.
That it didn't work out. The rest is none of their business.
I am not sure what you mean by "create" a partner. The minute you stop providing a narcissist with Narcissistic Supply - the minute you start criticizing him and disagreeing with him - he leaves and looks for alternative and more pliable sources of supply. I think it's possible anyone would do that if the old partner was clinging too long (why? WHY would anyone cling to someone who wants to leave them?). It's not healthy or laudable, but it's understandable. A Narcissist is more likely to invent an imaginary partner to make the old partner jealous either: a) To punish b) To reawaken the relationship If I understand your question correctly....YES! Maybe not invent from scratch but they will develop this whole scenario with someone they know... They start to talk about this person like they've known them all their lives....that all their exchanges were SO DEEP...etc... get rid of them