Male sexuality is highly driven by visual novelty, part of The pro-creative 'plan'. Males are programmed to impregnate as many variations of Females as possible to churn the gene pool and insure the appropriate variation of genetics in our progeny. As such, Males become easily bored and need new visual stimuli . . . hence, no end of porn.

the downside is that porn is addictive and can easily overwhelm the attraction of a now 'non-novel' familiar partner. Added to that, the porn preoccupies the deep thought and fantasy aspects of your partner. Secrecy and shame about whatever obsession is at the root of the porn fascination programs a male to experience pleasure in only the visual and situational presentations of porn.

The porn must be abstained from to restore sex drive and / or you must determine what your partner's fetish~fantasy thing is and you must incorporate some aspects of those scenarios into your 'real life' sex life to help him transition back to a normal reaction to you sexually.