Why do we long for sex so much?

[nonpareil]

Many males are genetically programmed to dislike their woman straying (don't want to raise someone else's children)
But will stray themselves with other women (spreading their genes- in their genetic interest)
Women don't like their male straying because he's spending his effort somewhere else and not concentrating on helping bring up her children (her genes).
Then there Is a theory, that some women may be attracted to alpha/uber males, have a fling and resulting child with them but return to another male who may make a better father.These things often being done subconsciously.
A woman has to invest far more effort in producing a child.
A male can spread his wild oats more freely with possibly no comeback to him.
Genetically , it has been in a males interest to wander and at the same time prevent his female partner from wandering.Hence the double standard.
Speaking on a purely biological level where the production of offspring is the goal.
Nice and romantic.