Sex, since the history of man or human evolution has gone through several changes, even in terms of definition and form and the individuals engaging in it. Once upon a time, sex was thought to be primarily for reproductive reasons, then for the relief of sexual tension and later, for the sexual pleasure.

Right from the explosive documentation of the Kama Sutra, various studies and experiences have been carried out by persons and institutions to unravel the mystery of human sexology and why, besides procreation, sex is important to mortal men and women. From the researches of Alfred Kinsey who is regarded as the father of sexology in the 40s and 50s to Masters and Johnsons famous researches on orgasms of the 60s and 70s, sex has become a subject of great interest to all. Now, a research conducted by psychologists Cindy Meston and David Buss on why women have sex which is published in the Archives of Sexual Behaviour, the duo in their new book of the same title, have listed 237 reasons why women have sex with their partners. Ranging from the mundane desires to experience physical pleasure; to the vengeful intentions of getting back at a cheating partner, the spiritual attempt to get closer to God, or the altruistic gesture of wanting a partner to feel good about themselves, Meston and Buss concluded that the motives for engaging in sexual intercourse may be larger in number than what most people think and psychologically complex in nature too. Some of the reasons listed are quite glaring and practiced across societies and persons at various times, regardless of their marital status too. In fact, marital sex as well as long term relationships tend to be more complex than those in newer or non-commitment relationships. Just as a married woman may have a legion of reasons for not wanting to have sex, she just might have another gazillion on why she must have sex. The most important and common reason being duty sex..... read it in full : http://gistandgossip.com/2016/02/must-read-why-we-have-sex/

Op, You did not tell us your own reason why you had sex last night.
Anyway, don't allow erec.tion to give you direction.....my 1% contribution.