Well, from what I've heard, the bible says yes it IS adultery.
Is a man who lusts after women other than his wife a heterosexual?
"Gay is a sick behavior that needs to be changed."
If you think so, I suggest you not engage in gay behavior. According to this post, you having gay thoughts (I'm not implying you do) will still be normal and heterosexual.
"You can claim it's my opinion and disagree, but you would be better served to listen and seek help."
Predictably: That's your opinion. I disagree.
No, the Bible does not anywhere suggest that lustful thoughts toward another man's wife deserves stoning. Jesus said, correctly, that sin doesn't come from external issues but form out of the heart. Same with the sin of homosexuality.
But you can only be judged by what you do, not by what you think. So a man who has sexual thoughts about other men is not gay. Only a man who has sex with other men is gay. In the same way, a man who dreams about robbing a bank is not a theif, only a man who robs a bank.
Both men should look at why they desire something evil. But neither is actionable by law.
Shalom.