I think that the cause is environmental...either a lack of proper parenting, or some form of sexual abuse when they are very young and unable to even remember the abuse...
and then, in some cases, it comes as they enter adolescence, go through normal fears of rejection by the other gender, and are approached by a homosexual who convinces them to try playing the other team...
and once they have played the game, it then becomes self-fulfilling because, like an alcoholic who knows they should not take another drink, they feel compelled to do it anyway...
once they have reached a certain point, I think it is virtually impossible to correct the problem. Like an alcoholic, they are compulsive and the only thing they could possibly do is abstain...
Or, we can just pretend they are normal, allow them to marry, teach young children that it is homophobic to refuse a date or approach from a homosexual, and see the numbers grow. (OK, that last line was sarcastic)
One of the efforts of the people trying to gay-ify our schools is to get every kid to consider the following question sometime during early adolescence: "If you've never had sex with someone of the same sex, how can you say you wouldn't like it?"
If I were 14 again and they asked me that, I'd say "You've never eaten dog crap pie either...how do you know you wouldn't like it?" Or maybe, "If they told you wolverines make good pets, would you believe them?"