Disappointed to hear this, but I understand.
Being in the same division was both frustrating and extremely fun. I know you definitely got the better of my teams, but I was always proud the few times I could return the favor. The truth is my teams would never have been any good without your contributions. I very much respect your willingness to share information and it has raised the competition in every league on this game.
I'm very much considering joining your new league, if for nothing else but to contribute to the data collection. However, I will miss the rivalry here.