There is no reason to think that the pleasures of sex would be completely spared the fate of the hedonic treadmill. Familiarity leads to boredom, and with it the incessant reduction of all pleasures that can threaten the sexual glue binding many couples together. While novelty is a sure-fire way of creating great experiences, the belief that matrimonial harmony depends on stability, fidelity, and constancy stands in direct opposition to this. As in everything related to satisfaction, and perhaps also relationships, the tension between what is predictable and safe versus what is novel and dangerous, is constantly being played out.
Satisfaction—that state of blessed contentment, mystical enlightenment, tranquility, a sense of something beyond your own existence—is ephemeral at best. Everything I have encountered inside the lab and out in the world suggests that satisfaction is not the same as either pleasure or happiness, and that searching for happiness will not necessarily lead to satisfaction. It is in the quest for satisfaction that you find it; within any quest you encounter novelty and your brain changes as a result. Novelty can take you far, but like everything, it too is subject to habituation, and the risks associated with pursuing novelty for its own sake may be substantial. How, for example, can you incorporate it into a long-term relationship?