First of all I want to say that we can all (for whatever reason) have times when we don’t feel for having sex or be intimate. This is completely natural. How we deal with it in our relationship differs of course. But in a relationship (no matter how it's defined) between two people loving each other, there will (even with some disagreement) be a natural need to care for and assure each other (empathy), and therefor find a needed compromise. Ultimately resulting in a mutual balance of expectations.
Mutual balance of expectations doesn’t exist in a relationship with narcissists – they don’t care what your expectations are! In short - they don't giva flying f*** about your needs in any way at all. And if they pretend they do (but evidently don't), it's just to make you keep up being their supplyment. This can, among many things, be identified through their twisted explanitions to why expectations, for one a reason or another, is irrelevant. Most probably he will accuse YOU of what a deficeint being you are as reasons to why he think you are making it very hard for him to have expectation with you. It sums up to that they live to control (at any cost) and this will of course - sooner or later - show in how they are in sex and intimacy too. And that's wether your narcissist is cerebral or somatic - he's a narcissist and that's your answer.
And here quoting Sam Vaknin (cerebral narcissist);
“Narcissists are either cerebral or somatic. In other words, they either generate their narcissistic supply by applying their bodies (somatic) or by applying their minds (cerebral).
It is a mistake to assume type-constancy. In other words, all narcissists are BOTH cerebral and somatic. In each narcissist, one of the types is dominant. So, the narcissist is either OVERWHELMINGLY cerebral - or DOMINANTLY somatic. But the other type, the recessive (manifested less frequently) type, is there. It is lurking, waiting to erupt.
The narcissist swings between his dominant type and his recessive type. The latter is expressed mainly as a result of a major narcissistic injury or life crisis.”
Sam Vaknin suggests that cerebral narcissists prefer living in celibacy even in a relationship – I do not agree with that. My ex narcissist was definitely mostly cerebral, but we had sex, though less and less frequently and in the end practically not. In the last 2 + years of our approx 5 year long rollercoaster relationship (living apart, living together, living apart, living together, living part for so many sick reasons), our sex life would slowly and safe pretty much mutate into an alien comparing with the first years, where we’d enjoy passionate and frequent sex in many (some sick) varieties. Even aside from him withholding it now and then, needing the high of control on that account, “no sex & intimacy” would be a huge contrast to our “normal”.
The somatic side of him would show up – as Sam Vaknin describe it – when it was needed to gain more control (supply). For an example when he felt I redraw from the craziness, and then he of course would screw around with other women and probably men too (it is suggested that cerebral narcissists are latent – hidden, not yet outed – homosexuals. I’m not sure I fully agree to that, even though my cerebral narcissist had several bisexual experiences).