已经接受的offer想反悔

现在已经接受TA offer但是现在想反悔。因为boston那边学校的offer来了。怎么操作？能否写以下内容。
Dear Prof.

I recently received the offer from ... Univ. I knew it is very unprofessional to accept the offer and decline it as it results in trenmendous amount of work to the admission committe, you and other applicants. I wonder whether I can withdrawl my acceptance and attend ... Univ instead as my partner is in the boston. I am deeply sorry for my action. I hope you and admission committe can accept my most sincere apology. Thence, I can go to school in Boston with my partner.

Thanks.