After 15-20 years I can understand it happening but a lot of people just do not understand, maybe you don't use names. I have done that before and I apologized and they were still upset and I just said that I was sorry that I am human and I make mistakes and I do not want to fight over it, if they were to turn it around they might make the same mistakes, we might be upset but if we love them we forgive them, everyone makes mistakes, it is not as if you are having a fling with your ex, like you said you barely think of him except that he is your ex and that you are happy that you have him now(this other guy) and their is no reason to be jealous or insecure about it, you are sorry and it was a mistake and that is about all you can say about it! Maybe someone else has some better answeres.
All the best to the both of you!

Thanks sandy. I feel the same way...Its nice to see someone on the same page as you.