Early desire is largely uncertainty. You do not know if they want you, so wanting them is charged. Once that question is settled, the charge changes — it does not vanish, but it stops arriving on its own.
Stop waiting to feel like it
For a lot of people desire arrives after things start, not before. Waiting to feel spontaneously in the mood can mean waiting indefinitely.
Distance is fuel
Time apart, separate interests, seeing your partner be good at something without you — these restore the small gap that wanting needs to cross.
Reduce the friction
Exhaustion, resentment about chores and a phone in bed do more damage than any technique fixes. Desire is usually the first thing to go and the last thing addressed.
Change one variable
Different room, different time of day, different order. Novelty does not have to mean anything dramatic.