I agree that homosexuality is not condoned by God..but one of the things you said in your post didn't make sense to me so i must not be understanding you right.
You said that a person who is gay cannot be Christian-i'm guessing because you mean that because a person is purposly choosing to do things that are against the commandments of God, then they cannot be Christian.
Yet, that statement doesn't make sense-how many people do you know who tell a lie, yet still consider themselves Christian, or that have sex outside of the bonds of marriage, or who covet things that others have, or who do not love their enemies, or who worships the idols of wealth or homes or luxury items...all of these things are spoken of in the bible as being sins and acts not condoned of God.
If we say, that a a gay person is not Christian because they are choosing to sin...then we implicate ourselves in that very statement-as we all choose wrong over right sometimes...