That is an important antidote to the idea that lower desire always means less love. Sometimes the issue is relational. But it may also involve fatigue, medication, pain, anxiety, depression, parenting demands, unfairness in household labor, or a lack of privacy.
Research on sexual boredom offers no simple formula either. Boredom is linked to desire and sexual satisfaction, but people in relationships of similar length can show different patterns. Time itself does not automatically switch erotic interest off.
The practical lesson is not that couples must constantly manufacture novelty. It may be more useful to treat desire as a sensitive system rather than a relationship test. What is pressing the brakes right now? What is missing—rest, safety, play, autonomy, attention, effective stimulation, or a sense of fairness?
Sometimes a couple needs a new script. Sometimes the answer is sleep, medical care, redistributing the workload, or an honest conversation. That is part of working with sexuality too: not demanding that the body produce desire regardless of conditions, but noticing the conditions that help desire emerge.