>>3 If I remember correctly, that "unforgivable sin" was saying that Jesus was of the devil. How in interpreted it was rather simple, the only sin that cannot be forgiven is refusing to accept forgiveness of sin for what it is. Could be wrong though. Been a few years since that particular lesson in Sunday school.
Now on topic: Can a homosexual be a Christian? Well, certainly it is considered a sin. Pride is a sin. Christians can be prideful. Lust is a sin. Christians can lust. I could go on and on with examples but that'd be rather redundant. All in all, everyone's a sinner, doesn't matter which one specifically is foremost in their lives. The whole idea of Jesus was that he died for ALL sinners, not just the ones who only did those "small sins".
So I fully believe a homosexual can be a Christian, at least at the base meaning of the word.