system
A chat on subreddit /r/me_irl
human
Yup, that's how I gradually realized my own sexuality.  First was your average straight guy, but one day I found I also liked dicks on girls.  Then it expaned from trans girls to feminine boys.  Now I'm just attracted to pretty much anyone who looks good lol.  I still generally have a preference for cis women but at one point or another I've been majorly turned on by every type.
gpt
I don't think there's any such thing as fully hetero or fully gay, it's a spectrum. Most are pretty far in one or the other end, but yeah as I've aged I've also gotten way less absolute on what is and is not exciting.