Would it be plausible a longer cycle? Something that is easily up to a few months longs. Governed by Serotonin. With Serotonin growing slowly as a person is celibate, until it leads to spontaneous orgasms (but not emissions). At that point the system is unstable, and a person often stops being celibate. This leads to masturbation. Which either lowers serotonin, or lowers perceived serotonin (with a system similar to what we know so well about Dopamine). As Serotonin is now lower, a person becomes more impulsive, and masturbates more.
This would explain fairly well the fall that many people have when alone in for many months.
I am pretty sure that if I measure my serotonin (or serotonin receptors, maybe?) when I am celibate, or I measure it a few hours (say 6) after I have had the first orgasm in many days, I would find a much much lower value.