Is Gay Okay?

So I was on www.gaiaonline.com debating whether homosexual acts are sinful, and I haven't been able to defend my point.

They say that in the Greek version of the Bible, the wording in 1 Corinthians 6:9 doesn't literally say "homosexual," thus what qualitifies as a sexual immorality is up to debate.

Leviticus says explicitly that you shouldn't participate in homosexual acts, but in the NT it says that Leviticus is obsolete because of Christ's crucifixion. (Colossians 2:14)

So premarital sex is wrong, but what if the married couple were of the same gender? Where in the Bible does it say that a marriage must be between man and woman?

I could use some help here.

But what if they're right?