Sex is a 3 billion year old tradition and it's not easy to break the worlds oldest tradition. Men are from the Earth. Women are from the Earth. People are having sex all the time. When we're not doing it with someone else we're masturbating.
Most men ejaculate daily.
This is the bodies way of getting rid of old sperm and making room for new fresh ones ready to get a woman pregnant. Women do the same thing so as to clean the lining of the uterus walls and to stay horny so that she'll be ready when the right male comes along. Since people are having sex on a daily basis, sex is happening all the time. The mail difference between a man having sex with himself or a partner is mostly location. Sex is life and all life, with the exception of viruses and some plants, comes from sex.