✔ 最佳答案
I regret to inform you that I have to tender my resignation from the present post for some personal reason. This will take effect as from the date we have discussed upon completion of the project or an earlier date if possible.
I shall be grateful if you could give me an employment reference in due course. Thank you for your kind attention.
(Note : It is not quite appropriate to say you will start up your business maybe on the business similar to your existing project.)