Narcissists chemically emit toxicity which infects you and chemically binds them to you.Hence the comment,I am not happy with her but can't see myself with anyone else.
Narcissistic personality disorder, is incurable and pills won't fix this.Part of the brain is incomplete so the person feels no empathy,no love,they are regressed to age 5 and behave like children.They know right from wrong but choose wrong for selfish reasons everytime.

The time you stay with your wife is time wasted in your life you will never get it back and she will continue to abuse you.I kept loving my family of narcissists for 35 years hoping they would love me back, no, they kept me under their control,sabotaged my attempts to build relationships outside the family and almost drove me to my death in order to inherit money from me.

I have only now broke free,I don't regret my life but one thing I have is inside out knowledge of narcissists,they all operate in the same ways,and you can't change them, you can't help them and no doctor can,they don't listen to anyone and they won't expose themselves to professional help they won't even admit they are the problem it is always you is the problem.You won't solve this.You say you can't watch someone you love crash and burn ,she won't,you will be the one all burnt out if you keep trying to help her.