You know, traditional sexual orientation terms get really confusing when you throw genderswapping into the mix. This is where clearer terms like "androphile" and "gynophile" demonstrate their utility.
Also, rather than them being "gay", maybe they're actually transgendered -- that is to say, the ex-girl/boy would've eventually discovered that s/he's actually a trans (wo)man, had the genderswap not happened.
... Say, if a trans man is into women, does that make him straight or gay? Again, another reason why I prefer "androphile" and "gynophile" as clear terms that do not depend on the subject person's sex.