From Daily Mail article:
According to the biggest study carried out into sexual motivations, these include that it is a "reasonably effective way of overcoming boredom", help you fall asleep or gets rid of a stress headache.
For others, the desire for revenge was the major factor, while some lovers were motivated by a purely selfless wish to make the other person feel good.
The researchers also confirmed what most already consider obvious - men and women think differently about sex.
They found it was more about the physical experience for men, while women's desires were based on an emotional need.
Women were much more likely to say: "I realised that I was in love." Men were more likely to say: "I wanted to increase the number of partners I had experienced."
Link to article