Aslamo Alaikum. I think in my mind that if I do "that" act again with in fifteen days my wife would be divorced for me. But I did it and broke my oath with in fifteen days. Nobody knows about this. I just think it in my mind not pronounce it. What is the status of my wife now.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If the matter is just thinking about this (divorce) and you did not utter it, then this does not lead to anything and this does not lead to divorce. Indeed, Allaah has forgiven this nation for the whispers which they have as long as they do not talk about it or act according to it, as confirmed by the Prophet . [Al-Bukhari and Muslim]

In any case, your wife is still considered your wife [the bond of marriage between you and her is still valid] but you should avoid misusing the words of divorce because its consequences will be regret in general. 

Allaah Knows best.