I completely understand... I think that similar could be said for any advanced degree. I'm all but finished with a BA in psychology, and I have no intention on settling there. I'm taking some fairly upper-level science classes as pre-medical preparation, so trust me, I'm with you on the self-doubt as far as whether I'm doing the right thing... Is it an option for you to do something else as opposed to continue with that, or are you sure you want to finish it out, or...?
maybe the problem isn't ALL the master's degree. maybe going to college not only out of state, but out of country was a lot to chew. you're away from your normal friends, your way of 'being' (when out of town) at 'down time,' and the expenses that you thought were all paid are draining you of resources.
maybe it's time to sit down with everyone involved in your situation. counselors, teachers, etc. and to work out a plan that will work better for you. mention your mental health situation - and the fact that a huge accompanying load and trying to do so much assistantship - is burning you up at both ends in terms of having the time to truly practice on YOUR music (after all - you are the one getting the degree) and that you need to reassess whether you can continue at the school if nothing changes. write down the things that you think would help YOU.