I wouldn't say anything to him. I think it stems down to jealousy and to be honest, I think it's pathetic that he is still hung up on this all these years later...I don't think people like that ever really get over that stuff, and nothing you say is going to make him see your position. I would be the bigger person, let it go, and I wouldn't even honor a letter like that with a response. The important thing is that YOU know why you did what you did, and the people who matter know why YOU did what you did...and because of that, your chapter turned around and a lot of people who wouldn't have been able to be a part of that brotherhood with him as president got to experience something great.
Congrats for all your hard work and turning your chapter around. That's admirable