It is natural for your sexual desire to ebb and flow, as you have described. It is unrealistic to believe that two people would not experience differences in their desires for sex. Lovemaking is an intimate activity requiring synchronicity of energy which is not always matched by your partner. More often than not, one partner is sexually aroused before the other. Unfortunately, possibilities can be stymied when partners expect instant availability, rather than an invitation to become sexually aroused.
Sexual arousal begins internally.
Heart rate, hormonal surges and other physical excitement follows a familiar, if not conditioned, pathway of sexual arousal in the limbic system of the brain. By the time a spouse has made a sexual overture to a partner, he or she has already experienced body changes. Their partner, however, may have other things on his or her mind. This can lead to feelings of intrusion, instead of invitation. Realistic expectations can prevent the interpretation that lack of immediate sexual response is a personal rejection.