I don't personally think anyone actively choose to be gay or straight. Many of the gay people I know do exhibit a lot of other psychopathology but some do not. This is also true of many of the straight people I know. So that's no real answer either.
Having a degree in Biology, I also know that many mammal species, if given unlimited food resources but limited living space, will expand their numbers until overcrowding is massive and then a huge amount of male homosexual activity will appear as a natural consequence.
So, I rather suspect it's built in to humans too. That's NOT choice.