The power of the imagination to recreate passion and desire and counteract sexual boredom is actually infinite, within the context of an otherwise strong relationship. However the gradual decline of sexual arousal in relationships is not uncommon. Sexual over-familiarity, or the onset of a feeling of repetitiveness in sexual relations between a couple, is one of the most frequent causes of physical and emotional infidelity and ultimately reasons for divorce lying behind relationship break ups.
This doesn't mean that there's some law of nature which says that couples - especially married couples - have to at some point stop finding each other sexually attractive. It's also not the case that when sexual desire seems to be being replaced by lack of sexual interest that there's no going back, that desire can never be rekindled.
Even if a couple have had sex together countless times and used every position in every circumstance and combination over years, it would still be perfectly possible, through the boundless power of the mind and the imagination, for them to be sexually attracted to each other, providing that the relationship was based on a foundation of love, compatibility and an ability to give and take.
If sexual over-familiarity is starting to have an adverse effect on your relationship, and assuming that the relationship itself is valued by both partners, then it's time to focus on what to do about it.
Firstly, experimentation with fun sex games, different clothing, locations - use your imagination - can start to arrest the decline of mutual sexual interest.
For some couples swinging - though definitely not suitable for all even if both are initially willing - has nevertheless been known to strengthen and revitalize some relationships. Alternatively, the technique of mutually agreed temporary abstinence from full sex, but continuing to indulge in mutual stimulation stopping short of penetration, ejaculation or orgasm can, say after a couple of weeks or so, bring about a rekindling of desire between partners.
Secondly, following these options up with each partner's use of a hypnosis pc download or mp3 themed to stimulate the libido, followed by experimentation with different lovemaking positions and perhaps g spot massage, will recreate erotic excitement in an otherwise good relationship. The dampening of imagination is what is responsible for sexual boredom. It follows naturally that by revitalizing the sexual imagination through self hypnosis a couple will rediscover the erotic pleasure and satisfaction which they truly wish to give each other.