Mark Hamill has given his support of Luke Skywalker having whatever sexuality you, the fans, damn well please. In a quote in the Sun he said, "fans are writing and ask all these questions, ‘I’m bullied in school... I’m afraid to come out’. They say to me, ‘Could Luke be gay?’ I’d say it is meant to be interpreted by the viewer. 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."
Back in January, he echoed that same sentiment to a fan on Twitter who asked if Luke Skywalker is bisexual. Hamill told her she could decide for herself since his sexuality has never been addressed. Now, Mark Hamill isn't exactly the be-all, end-all decider of all things Luke Skywalker, but your slash fic is officially blessed by Hamill himself.