Not to get all semantic about it, but “gay,” “homosexual” and “homosexuality” as terms get collapsed in a way that’s almost inevitable, but not necessarily appropriate.
“Gay” is an identity, and so is less descriptive than people often consider it and is also, when we consider it as an identity, something that is arguably completely fluid and one day will become an anachronistic term. Being gay right now has a very, very important social function – when someone says that they’re gay, they are telling people that their homosexuality is not damaging, not shameful, and not to be questioned. What two people, of consenting age, mutually agree to to give themselves and each other pleasure should not be a social issue – but when someone says “I am gay,” he or she is pointing out that their are social assumptions, pressures and oppressive mechanisms at work that require them to stand up and say “No.”