The New Joy of Sex: Part 3. A Lover's State of Mind and Soul. 2008, based on the works of Alex Comfort and Susan Quilliam. Listen to the podcast at How To Sex. Hormones. The fuel in the sex machine, keeping desire, arousal, and performance ticking over, as well as driving affection and love. For the most part, they form a constant underpinning of mood, supporting though never replacing the honest-to-goodness sexual diesel generated by enthusiastic lovers. A peak or a valley, on the other hand, can impact. Sexually, the crucial fuel is testosterone, for her as well as for him. His will peak during his twenties, then settle into a more or less consistent pattern, dipping over the course of a long term relationship and rising in a new one; no excuse for straying, but a possible explanation of the temptation to do so. With age, it will gently decline; but rarely enough to cause problems; if his erection is failing, that’s reason for action, not resignation. In her, testosterone h...