From Robin Waterfield's "Athens - From Ancient Ideal to Modern City" He's a prolific Greek Scholar.... translated about 20 ancient greek texts, very respected.
"It was accepted that at a certain time of his youth a teenager had a kind of beauty, and that older men would be attracted to him; ancient Athenian homosexuality was in fact pederasty in the literal sense of the word. If an affair took place, it was monogamous (there was little homosexual promiscuity) and generally lasted only a few years, as long as the boy kept his youthful "bloom," as the Greeks called it. Lifelong homosexual relationships between men were extremely rare, though the pair were supposed to remain friends even after the sexual side of the relationship had died down." Homosexual relationships between women were also temporary, even fleeting. Athenian homoeroticism was largely an upper-class phenomenon, for two main reasons. First, any soceity which represses women as much as ancient Athens did runs the risk of forcing it's members to find other outlets for their sexuality. The second factor concerns the somewhat ritualized expectations of a homoerotic affair. A good-looking boy who was in bloom would be pursued by several older men. These older men were the ones feeling passion, and one of them would be successful if he could induce the boy to admire him. This was manly enough to be acceptable, but boys were not expected to flirt to attract lovers, becase that was regarded as too effeminate, so sex was generally limited to masturbation or intercourse between the thighs. The boy would most likely feel little or nothing beyond a degree of excitement. He was expected merely to "gratify" the lover, as the Athenians tended rather delicatedly to put it. What the boy got out of the affair - and this again is why it was an upper-class phenomenon - was a form of patronage and mentorship. In return for granting his sexual favors, he would expect the older man to act as an extra guardian in public life, to introduce him into the bst social circles, and later, perhaps many years after the sexual side of the affair was over, to help him gain a foothold in the political life of the city; this would seem especially attractive to boys from poorer households who were eager for advancement."