There are numerous types of serotonin receptors within the brain, each producing its own unique effect. Sexual arousal and inhibition affect different types of serotonin receptors. Animal studies have shown that serotonin is one of the neurochemicals that create sexual satiety.
Animal studies
Hormone-neurotransmitter interactions in the control of sexual behavior
Lateral Hypothalamic Serotonin Inhibits Nucleus Accumbens Dopamine: Implications for Sexual Satiety