Pages that delve into this a little more:

• Stanford Encyclopedia of Philosophy
• Wikipedia
  • "A common thread of constructionist argument is that no one in antiquity or the Middle Ages experienced homosexuality as an exclusive, permanent, or defining mode of sexuality. John Boswell has countered this argument by citing ancient Greek writings by Plato, which describe individuals exhibiting exclusive homosexuality."
  • John Boswell
  • Same-Sex Unions in Pre-Modern Europe
  • Adelphopoiesis
• /r/AskHistorians FAQ additional items:
  • In a CNN interview a few years ago, Sir Ian McKellen mentioned that "some of the earliest marriages conducted by the Christian church were between men" and homophobic attitudes are "sort of Victorian". How much does this hold true? — 130 comments, 1040 points
  • What is the genesis of anti-homosexuality? — 77 comments, 236 points
  • Does it make sense to talk about "sexual orientation" in the ancient world, given the large differences in how sexuality was approached? — 31 comments, 138 points
  • Are there any noteworthy example of tolerance towards homosexuality in the Medieval Age? — 3 comments, 13 points
• "Why Heterosexuality Didn't Really Exist Until the 19th Century", at Alternet