The little red hen decides one day to bake some bread. She is gathering up flour and yeast and all the ingredients. She asks the dog if he wants to help carry the flour, but he declines. Asks the duck if he wants to help knead the dough, but he declines. Basically, nobody wants to help make the bread. However, when the bread is finished and comes out of the oven hot and fresh, everybody is more than eager to eat it.
Socially and psychologically, it may be difficult for some individuals to deal with sex outside a safe and committed relationship. Sex acts as all kinds of emotional/psychological/endocrinological triggers. It can lead to one one hand guilt, sorrow, reduced self-image, and even addiction/compulsion, but on the other hand lead to serenity, well-being, compassion, confidence, and joy.
Another situation I notice is when either the girl or the guy is a lot older and a stronger personality-wise and finds it easy to totally manipulate and control the other.
Basically, a lot of relationships these days are supposedly just ‘friends, with benefits’ where both parties know that they are only with each other for sex. I think this is perfectly plausible as long as both parties understand what is going on.
Using occurs when one person does not regard the other as anything beyond a means to an end. Two people in a sexual relationship can mutually use one another, although the term is traditionally associated with a one-sided deception (deception is not a requisite, either).
I would say using someone is when you use them to get something you want. When you don’t care about the person, or what they think or how they feel, and you just care about making yourself happy.