Actually, it's not my opinion.
Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers, will inherit the kingdom of God (1 Corinthians 6:9-10).
Now let me clarify.
It is possible for a Christian to struggle with homosexual temptations.
Whether or not these desires and temptations exist does not determine whether a person is a Christian.
What differentiates a Christians life from a non-Christians life is the struggle against sin. A true Christian will always repent, will always eventually return to God, and will always resume the struggle against sin. But the Bible gives no support for the idea that a person who perpetually and unrepentantly engages in sin can indeed be a Christian.
Clarifying futher, if the phrase homosexual christian refers to a person who struggles against homosexual desires and temptations yes, a gay Christian is possible. However, the description is not accurate for such a person, since he/she does not desire to be gay, and is struggling against the temptations.
This person would not be a struggling Christian, just as there are Christians who struggle with fornication, lying, and stealing. However, if homosexual christian refers to a person who actively, perpetually, and unrepentantly lives a homosexual lifestyle no, it is not possible for such a person to truly be a Christian.