It sounds like fun!!! Some day we'll do the same together!
I'm sure you can compose a short, sweet, to-the-point note. I think giving them an opportunity to reconsider their position is the 'right' thing to do. Who knows, maybe it would open the door of communication and you may be able to give him another chance....? I guess that would depend on how much of your trust he's broken, and whether or not he can regain that trust. If you send the letter, the ball would be in his court. If you are even interested in entertaining that idea, that is.
Just my 2 cents. You do what you feel is best. Of course you have my support either way.