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I have accepted a scholarship at a certain university, after exchanging many emails with the supervisor. I was interviewed by him and he personally took trouble to secure funding for me. And he also helped me a lot throughout the process. But now I have received a better offer from a better university, which has a better research group.
Now I am not sure how to email my supervisor rejecting the offer, after accepting it months back. It seems a really unethical thing to do. But considering all the other aspects, the second university seems to be the ideal choice for me.
How should I reject the first offer without offending my supervisor?