My uncle dave caught the gay once, he was happily married and out of the blue he turns queer . True story
You should probably have a conversation with your uncle. He didn't catch anything, he was already there. He may have been happily married, but clearly he missed having a homosexual relationship or he would have stayed married.
Incidentally, if you could "catch the gay once" like it is a cold or some virus, wouldn't you eventually recover?
A lot of gay folks enter into heterosexual relationships because they want to appease their families and/or they are in denial. The problem with doing this is that it doesn't change who they are. While it is possible for someone to not act on their sexual preferences, it is not possible to deny how you feel forever. Eventually people in these situations, like you uncle, come out of the closet....hard!
I am bisexual. I realized this when I was still a teenager. Had it been an illness, I would have gladly been vaccinated against it, because being gay or bisexual was and still is fraught with issues of acceptance and self-esteem. I don't know anyone who would willingly choose to be gay.