Following his marriage to Emily Bushman in 2006, Brandon Sanderson and the latter have been together ever since. Between them, they have three sons.
Emily serves as both an educator and his business manager. Other than that, not much—if anything—is known about his prior relationship(s).
As someone who identifies as straight, Brandon Sanderson is neither gay nor bisexual. He was married to Emily Bushman in 2006, and the two of them had three sons together.
Other than that, nothing is known about his prior romantic relationships. His past relationships suggest that he is a straight, one-woman man.