Enjoy the decline, but carefully? A recent study should be a wake-up call for men and women.

From a study in the BMJ Sexual and Reproductive Health:

Having had 10 or more lifetime sexual partners was associated with higher odds of reporting a diagnosis of cancer than having had 0–1 sexual partners in men (OR 1.69, 95% CI 1.01 to 2.83) and women (OR 1.91, 95% CI 1.04 to 3.51), respectively. Women who had 10 or more lifetime sexual partners also had higher odds of reporting a limiting long-standing illness (OR 1.64, 95% CI 1.15 to 2.35). No other statistically significant associations were observed.

In simpler terms? In men, having 10 or more partners is associated with a 69% greater chance of reporting a cancer diagnosis. In women, having 10 or more partners is associated with a 91% greater chance of reporting a cancer diagnosis, and a 64% greater chance of reporting a limiting illness.

No causality has been established, so it's entirely possible that two distinct things correlate with having a greater number of partners. Study subjects were "2537 men and 3185 women aged ≥50 years participating in the English Longitudinal Study of Ageing". The risks were adjusted for socioeconomic class, demographics, and health-related covariants.

The bottom line? Wear a condom. Weight risks and reward. There appear to be long term consequences of having many partners. Since the cause is unknown, the fact that you didn't catch an STI may or may not have an effect on long term risk.