I'm more on the literature side of classics than the sociological side, but one thing I find interesting about the Roman attitude to sex and orientation is that they make the crucial distinction not between hetero- and homosexual, but between penetrator and penetrated. So, a high-status Roman male could do whoever he liked (my high-school Latin class, when we got hold of a complete Catullus: 'Mrs X! You never told us Catullus was bisexual!') as long as he was on top/being blown. Which is a difficulty for equality in m/m relationships - possibly that explains why I tend to prefer non-explicit fic. There's a bit more leeway in Greek and Hellenised culture, but not much.

(And, just because I never get sick of it: the Warren Cup (http://www.thebritishmuseum.ac.uk/compass/ixbin/goto?id=OBJ5831). Also, textbooks never seem to mention f/f relationships in classical culture outside a coy allusion to Sappho, but I saw a lovely f/f Greek black-figure vase painting exhibited alongside the Warren Cup.)