Beyond that, Luke did settle down and marry Mara Jade in the Expanded Universe stories, so there’s precedent to pull from if the folks behind the big screen Star Wars franchise ever decide to return to that creative well to create some of those “untold stories” Mark Hamill’s tweet refers to.
So, it’s not outside the realm of possibility to imagine that Luke may have found love at some point after the defeat of The Empire.
Though romance is strictly forbidden under the traditional Jedi code, it’s worth noting that Luke’s own training as a Jedi was very unorthodox, which means he may have decided that the celibate life wasn’t for him.