No offense, but did you not know that the job being offered was in a small town where there is nothing to do? My guess would be you did. So, on some level of professionalism, you do owe your employer something - especially if they have been kind to you. Exactly what that is really comes down to you and what you consider to be professional and acceptable behavior.
You are going through what most of us low time pilots have gone through at the beginning of our careers - accepting the job that is less than perfect in order to boost your career and open more doors. So do that. Stay as long as you within yourself feel is acceptable to repay the favor while keeping your career goals a priority. Once you get a better job offer, kindly notify them, thank them for an opportunity and give them time to find replacement. Then leave and continue your career elsewhere. Good luck