Should my boyfriend answer the real reason he is relocating, if he is asked during a job interview?

In two weeks, my boyfriend and I will be relocating from Philadelphia, PA, to Durham, NC, because I will be attending graduate school there. My boyfriend is in the process of finding a job in NC, and in his cover letters, he simply mentions that he will be relocating at the end of the month. Obviously, he doesn’t have to answer if they ask “why” in an interview, but sometimes, interviewers take a more casual approach, and that sort of thing could come up. On the one hand, it makes him sound like a committed person because he’s moving for me, and maybe it also sounds good that he scored a smart girlfriend. On the other hand, potential employers could worry that he wouldn’t be living in NC permanently or that he’d go back to Philadelphia if we broke up. How should he handle that question if asked?