No formerly straight, bi or gay people I know of.
One of my mates, who is 25, has just decided to let us know he is gay
but he was always gay. He was just too scared about what we might
think to admit it.
If I woke up tomorrow and thought I fancied sex with a man, that would
probably make me formerly straight, since the very thought of it is
incredibly unpleasant.
Even then, you could argue that I'd just been in denial all this time.