A fan recently tweeted Mark Hamill (aka Luke Skywalker) asking about Luke's sexuality. In the spirit of sexual fluidity, Hamill responded:
Huffington Post smartly anticipated everyone's follow-up question: Can this theory apply to all characters who don't explicitly state their sexuality?
Nerdist writer Eric Diaz aptly notes:
"Luke Skywalker, on the other hand, has shown almost zero sexual interest in anyone in any of the films...with the exception of a woman who turned out to be his sister. And even then, that interest seemed considerably mild. So Luke is a much stronger candidate for being a character that can go in any direction. That doesn't mean Lucasfilm and Disney will ever bring it to the screen, of course, but it's good to know that the man who brings the character to life would be completely cool with the notion if they did."
It looks like we'll never get a clear answer, but who cares. Star Wars is progressive like that.