This sounds like a conversation my partner and I had a few weeks back. He is in the same boat, only he actually got the job. Problem is, the person who hired him to teach was one of his old teachers, and knew that he was married to a woman. It doesn't help that the country we are moving to doesn't exactly smile on openly same sex relationships. He felt the need to disclose to his new boss about me, so that in the mind of his coworkers, I will be seen as just a very masculine woman. Sadly, since it's Japan, if he says anything I would be expected to play at being female. It doesn't help that gossip is a national sport there. -_-
So, yes, I understand your concerns very well. We ended up making a deal. If the time came when he needed to tell his boss then I wouldn't blame him, but until that time arises, we are not going to mention it. We are going to just continue living and if it happens to come up, play it off as something that we don't even consider out of the ordinary and therefore not in need of explanation. That being said you are in a different situation. I will be in a huge city, you will be in a small town. Small towns in my experience are not the picturesque little places people make them out to be; gossip spreads faster than the flu in an elementary school.
I don't think you should be in the situation where you have to be outed. His choice of partner should have no bearing on getting the job. However, I know that isn't how it works in actuality. I think you have a right to expect your privacy to be kept. No one needs to know anything about your medical past or about you and your partner's personal life. I mean, people don't disclose having high blood pressure or a bad relationship with their mother in interviews. So why bother mentioning anything about ones SO? If it does come up and he tells his old buddy, I would say that he needs to stress the fact that you feel concerned about it getting out.
Honestly though, I know the feeling of worrying over whether your partner is going to out you for a job. I don't see that he needs to, and he could probably keep it to himself. Besides, his outing you is like apologizing for you being in his life and causing someone else mild to no discomfort for like, a minute. In the end, when I said that to Joe, he agreed that he wouldn't out me unless his job was on the line or I gave him permission on a case-by-case basis.
I hope you two can come to an agreement. You shouldn't have to have your privacy violated. He wouldn't tell his boss or buddy anything about his relationships with siblings/parents in an interview or during discussions for jobs, so why would he bring up his partner?