I've mentioned on other threads that sweating is a natural reaction to mating. With elephants it is called "musting" where the animal sweats pheromones behind their ears to attract a mate and let them know they are in heat. Many people do much the same thing, but it is misunderstood as merely sweating. While some of it is perspiration from the exertion, a great deal of it is to reflect their level of arousal and to increase the level of arousal in their mate. It's so hot when the guy uses his wet body to cover his lover in his sweat, essentially marking him as his.