The thing that is fairly new to Western society (and I would argue most non-Western societies) is the idea that sex is an activity that happens between equals.
A free, high status Roman man generally did not have sex with an equal - his wife, slaves, younger boys or men, and lower status free men certainly did not qualify. In fact, sex between male equals was looked at askance. "Roman Homosexuality" by Craig A. Williams is a brilliant book on this topic - he argues that degrees of free, unfree, dominant and submissive (and not the consenting, negotiated bdsm versions) are the critical categories, not hetero- and homosexuality.
*Now removing historian of sexuality hat*