They need to satisfy their sense of control. For instance, if you "dare" have another friend (other then the narcissist) then, he will be a better friend then you are to that friend. All of it is to escalate self importance and minimize the value of your friendship. Narcissists hate authentic relationships (because they've never had one) but are very good at mimicking them for the purpose of pretense and control of one's (anyone's) emotions.
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.
When they need something from you....
You can't. Part of being a narcissist means that they cannot possibly be wrong/disordered/need help.
Yes anyone can be a supply for them,anyone that is Not a narcissist ,and to be a victim you just need to be a human being with feelings.
You answered it yourself... he is your ex, but not ex-narcissistic. he will always have the need to see himself as the center of attention. it has nothing to do with you, only himself.
Because he is a callous and uncaring narcissist. Forget about him and find a decent person.
A narcissist doesn't care about anyone other than themselves. When this person is finished with one person, that person no longer matters. They move on and it doesn't matter with whom (friend or someone you don't even know).
The main trait of a narcissist is that they see and perceive things only as they pertain to themselves. So if a commonly held truth doesn't correspond to the view of the narcissist, the narcissist will need to create a version of the truth which does.
"A friend in need is a friend indeed"
A borderline. Essentially a more emotionally reactive narcissist.
The narcissist only wanted needed you to supply their need at that time. Now they have the contract job they don't have a need for you until you have something else that they want that is when they will need you again. If you don't have anything they want to nourish their narcissist supply the have no problem writing you off and forgetting that you ever existed. They have no empathy RUN do not stay in contact with them they will destroy you.
Cbt approach in terms of looking at safety behaviours/ defenses would be useful. The narcissist would need to have some insight and willing to change as with any therapeutic approach. The therapist would need to be very boundaried and not open to manipulation. Session homework should be contacted in. Where there are long term issues of childhood the narcissist may wish to explore psychotherapy although at some point they will need to be willing to change and narcissists often don't want to change. (Why would anyone if they get immediate gratification and addiction fed). However, for those narcissists that acknowledge the pain they put others through and want some continuity in their lives, therapy is an option. Even more so, the victims of narcissist abuse need help through the post trauma of the narcissist abandonment, and to learn to adhere to the no contact rule for their own sanity! The narcissist's return is never because they love you, no need to play detective, just accept you are one of many addictions, an object to play with until they start the cycle again. If you have emotions you won't be able to stay in a relationship with a narcissist. As Sam Vaknin has said, mirror the narcissist, but to do that you have to be non- emotional and acknowledge that he projects his own inadequacies onto you, blames you for the very things he does, plays on your guilt, lies and cheats. If you can avoid internalising this and give to the narcissist and have your own needs ignored, then you need to look at your self esteem. Do not lose yourself to a figment of your imagination, keep a journal of the narcissist behaviour, and move on. The narcissist will be hurt to see you move on, and happy as they have no control and that liberation will empower you.