Hi Arnold,
To diganose your wife, a therapist would have to see her, she'd have to cooperate, then the counsellor must find it OK and safe to tell her of the diagnosis (most NPD counsellors are biased against it, since they feel that it gives them better therapeutic access to just feed their clients illusions and go from there. THEN she should be willing to tell you what that diagnosis is, since according to confidentiality rules teh counsellor would not reveal it to anyone else. What are the chances of the joint probability of all the ifs holding up? I would say statistically zero.
There is another route, which most of us found. Through our own therapist, who told us about NPD and told us that ou parents/spouse may have it. Then there are some brave souls like you who found it on their own, and prefer to work on their problems independently.
If you feel that your spouse has NPD, then I'd say chances are that 99% she has it, especially because you say that you are a shadow of your former self. This is a clear giveaway.
As for helping her, most of us have learned the HARD way that they cannot be helped. So there is noreason why you should not choose the road well travelled too.

However, if you want to learn from others' experience, go into it with your eyes open, hope for the best but do prepare for the worst. If you ever confront an N, they will rob you, steal you, slander you, turn your loved ones against you. If it stops here, consider yourself lucky. So be prepared with your finances (e.g. if you have joint accounts, transfer the funds,) make plans to protect your children, etc. You may have accepted that you'd split these properties with her, but don't be suprized if she controls all of them 100% while you twiddle your thumb. If she has the power to do so, she most likely may. (My own Nmom did this to me!)
One critical peice of advice. YOU must control the timing of when you leave her. That means not letting it on before you are fully prepared. Remove fmily pictures, any other items that mean a lot to you from teh house before you do so. Ns are VERY likely to posssess and control and destroy such things.
The oft repeated advice is that you'll find out what teh narcissist is up to by listning to clues, by paying atention to what is it that she is accusing you of. If she accuses of you of theft, then that is what she is planning. If she accuses you of slander, then that is what she is engaging in.
Also, DONT expect your family or friends to entirely understand your ordeal. Only those who've had bouts with Ns can offer you true empathy. That is why many of us hang out here, even years after Ns have exited our lives.
Arnold, let us know how therapy goes. All the best.
Marta
My two favorite links for NPD. The first one is a must read academic paper.
http://www.ippnj.org/mcwilliams1.htmlhttp://www.operationdoubles.com/narc/http://www.chameleongroup.org.uk/npd/index.html