The Star Wars movies are relatively tame, sexless affairs—there's a touch of romance, sure, but most of the characters might as well be entirely sexless. We don't know anything about the orientation of say, Lando (probably the most omnivorous lover in the entire saga) or Chewbacca (although Maz Kanata has a thing for him in The Force Awakens). As a franchise with its origins as a couple of movies for kids in a less progressive era, sexual representation just wasn't a thing it had in mind. In 2016, however, it's very much at the forefront of the conversation—J.J. Abrams himself promised last week that gay characters were coming to Star Wars.
But, as we just alluded—we don't know a whole lot about the proclivities of many Star Wars characters. It could be, then, that some of them are already gay. Like Luke Skywalker.
According to The Sun, Mark Hamill is totally down with the idea of a gay Luke, saying there's nothing in the films specifying the Jedi's sexuality, so he certainly could be.
John Boyega has confirmed that the very, very, very subtle love story between his Finn and Oscar Isaac's Poe Dameron is, indeed, imagined.
"I’d say it is meant to be interpreted by the viewer," said Hamill. “If you think Luke is gay, of course he is. You should not be ashamed of it. Judge Luke by his character, not by who he loves.”
Some might take issue with Hamill's comments, since Luke clearly pines for (and kisses) Leia, but he also finds out they're siblings. While we're not sure that's exactly How It Works, maybe that moment really helped Luke figure things out? He's definitely not interested in women (or anyone) by the time Return of the Jedi comes around.
What's really interesting, though, is the fact that Hamill is essentially advocating for what's known in fan communities as headcanon. Headcanon is a term for the bits of backstory fans invent and believe because there's nothing in the text to refute it. For example: It is my personal headcanon that Boba Fett is a huge fan of Magic: The Gathering and uses Tinder to promote the campaigns of his favorite politicians, and there's nothing you can do to refute that because there isn't a damn thing in the movies that proves otherwise.
In summary: If you want Luke to be gay, then yeah, he's gay. If not, that's cool too. There's no definitive answer from the films at the moment, although it would be pretty great if Luke's first line in Episode VIII was a specific description of just who, exactly, he would like to sleep with.