I wonder if we'll ever actually know 100%. The in-utero hormonal thing sounds pretty interesting but i dont think they know for sure (?). We're probably better off not knowing, if we did im sure people would see it as something 'fixable'.
For the "fix" part I heard of a therapy or something like this which has worked to an extend in turning people hetero and was banned for being immoral and bad for the one threated. It has worked on the same principle as when one goes queer because of a mental trauma. Good luck on anybody who waanna try it .
There's a program in my city that's getting tons of news coverage because they put a billboard up saying something like, "don't want to be gay anymore? Call us for help." They try to make people don't wanna be gay anymore "straight." Someone vandalized the billboard and everyone has been raising a huge uproar about it but the business doesn't care. Crazy stuff.
What's really sick about these businesses is they actually offer false 'hope' to those impressionable younger people who are unhappy about being gay, usually because of their parents views or religion or whatever preventing them from accepting themselves and it makes it so much worse for them in the long run when it inevitably fails. There is a reason why so many people who've undergone these 'therapies' are speaking out against them compared to the very few who are willing to speak in support. Even those who initially believe they have been successfully turned straight usually end up accepting that isn't the case later along the way, often after they've gotten married and had kids whom then have to suffer watching their parents unhappiness as well. Incredibly unethical.
There's a lot of theories. 'The Nature of Things' actually did a really really good episode looking at biological explanation for homosexuality (in men anyways) which I BELIEVE was called 'Survival of the Fabulous', but I could be wrong. I bet there's somewhere on the internet that you could watch it though. There are links to in-utero hormonal exposure, genetics, physiological differences in the brain..... there's no definitive answer yet, and it could be a combination of things, but there's a lot to support the idea that its biological.
