What I should write to a professor to decline a PhD offer, while I have accepted it months ago? In Dec. last year, I got admitted to CUHK as a PhD student, and have chosen my 'future advisor', with whom I had been emailing for several months. Three months later, I recieved HKPFS (Hong Kong PhD Fellowhship Scheme, HK$20,000/m, big award). Currently, I'm waiting for the result of visa application. If nothing happened, that's the university I would like to go, for the award and its academic achievement.

However, after the time having accepted the admission offer, I met a few guys, and  gradually realized that I am homosexual and what I want is a place to live freer. I also have applied several American universities before CUHK's interview. Two weeks before, an offer was made by one of them. From my birth, I have been living in Mainland China. This could be an opportunity for me to seek a change in my life - date a guy and get married eventually. So, after months of struggle of my identity, choosing which university to go is not a problem. No matter how CUHK outperforms the american one, I would like to go america. 

So, the question now is what and how I should write to my CUHK advisor? I know making excuses untrue or creating 'irresistable event' is not a wise idea. But telling him that I am homosexual and decide to go america instead would make things better? CUHK has rather early admission, and they have made all the admissions long time ago. I think they would get mad/annoyed no matter how. :(

Another problem is that my teachers from my undergraduate college heard about my story. (They thought why I chose America over HK is that I have a crush on a girl there. But the rest they know is the same as the truth.) They all want me to write back to CUHK asap. So, what I should do these days to make them not thinking less of me?

My problem is not typical. I'm not serving 'being homosexual' as an excuse. I know many people are not OK with it. But it's the truth I have to deal with. Any advice is appreciated, :)
I would suggest writing something like this:


  For personal reasons, it turns out that I cannot attend this university after all; I will be moving overseas. I am sorry I will not be able to work with you. Thank you very much for your time. I apologize for the inconvenience and late notice.


It is possible that he may be a little disappointed or annoyed, or  suspect that you  are moving because you have another offer that you prefer for academic reasons, but I don't think it should be a huge deal. You've exchanged some emails, but it isn't as if he has invested years of his time in working with you. It's generally not a good idea to go around alienating people in the small world of  academia, but I don't think one slightly annoyed professor will cause any real harm to your career. Anyway, clearly this decision is important enough to you that it's worth the risk.

It's possible he would be more understanding if he knew the real reason. It's your decision to whom you want to come out, and I can't offer any advice on that. But you should only tell him if you're really comfortable with doing so; I don't think the academic consequences of keeping it private are significant enough to enter in the decision.

The phrase "personal reasons" is intended as a polite signal that you don't intend to discuss those reasons, and that it would be rude for him to press you. There is some cultural context there (I am in the US) so it's of course possible he won't take it that way. If you know a better way to express this to him, by all means use it.  If he is rude enough to demand more information than you want to share, you can just repeat that "it is a personal matter".