Milord Sex is at the base of Maslow pyramid. While this as been criticised, in the author intention is definitively there. It’s a basic need. Sometime you will not see in the diagram, but it’s basically there
Also interesting to see that while sex is among physiological needs (with food and sleep), love, intimacy, are on the third level, so higher, where needs there are needs for belong.
From that same article:
Regarding the structure of his hierarchy, Maslow (1987) proposed that the order in the hierarchy “is not nearly as rigid” (p. 68) as he may have implied in his earlier description.
Maslow noted that the order of needs might be flexible based on external circumstances or individual differences. For example, he notes that for some individuals, the need for self-esteem is more important than the need for love. For others, the need for creative fulfillment may supersede even the most basic needs.
I would say sex in particular is one of those needs that is rather physiological in nature, but not important for the survival of the individual the way food, drink or shelter are. For the species, sure, sex matters as the vehicle of reproduction, which is why most humans experience a certain urge to engage in sexuality when they are equipped to meet the basic needs for potential offspring. But also, sexuality often serves as a supplement to love and intimacy for many, and a lot of people had a very good experience living fulfilled lives with minimal physiological sex.