Praise be to Allaah.
Your saying to your wife, I swear by Almighty Allah that if you speak about this matter again it will be the last thing between me and you is not an explicit statement of divorce; rather it comes under the heading of implicit statements that may be understood as referring to divorce or may be understood otherwise.
The basic principle with regard to implicit statements is that they do not count as divorce unless there was the intention of divorce, even if they are spoken during an argument or in a moment of anger, according to the more correct opinion.
Please see the answer to question no. 136438
Based on that, if you did not intend divorce when you spoke these words, then no divorce has taken place.
But if you did intend divorce by these words when you said that, then divorce has taken place if she spoke about that matter, and it counts as one divorce. If she did not speak about it then nothing has happened.
If a person says words that imply divorce but he is not sure whether he intended divorce or not, then it does not count as a divorce because the basic principle is that no divorce has taken place.
As you are not certain whether there was any intention of divorce; rather you think it most likely that you did not have any such intention, then no divorce has taken place.
And Allah knows best.