When someone has an affair, regardless of their sexual orientation(Gay, Lesbian, Bisexual, or straight), it is called an affair.
"gay man" is the best English term there is.
It is a derogatory term for an effeminate gay man.
It can either mean that someone is a coward, or it can be a gay term for a very young gay man.
Husband. A gay man is still a man, even when he marries another man. If a man expresses his gender as female, than he is transgender and that is an issue separate from being gay.
Whether the affair is with someone who is straight, gay or bi makes no difference. It's still an affair and the law is the same.
Such a person would be a gay man. Homosexual is another term for this.
The slang term is Fish-Wife.
Yes. If you can prove he had an affair and had an affair with another man, then you have grounds for divorce just like if the man was cheating with another woman. Unless of course it's a "gay" marriage, then I think that would defeat the purpose don't you. The same above would also apply if the spouse is female and is cheating on the man with another woman.
A person, man or woman, who has an extramarital affair with another person, man or woman, is called an adulterer.
A gay person can be a man or a woman. The term is used for both genders. Gay women can also be called lesbians.
The slang term is a "beard."
The term gay is when one man has gay anal butt sex with another man. This is only considered gay if the scrotums touch each other. This is one of my favorite activities, as I do not like vaginas.