I'm so sorry you have to deal with this! My parents really did split because one of them was having an affair, my father as it happens. As a teenager, discovering that reason knocked me for a bigger loop than the divorce, which was plenty traumatizing all on its own.

If I were your son, I would probably really need to know that no affair was happening.

I think a sit-down with your son, premised on the notion that he's a little older now and can handle a more mature conversation, might be in order.

There's a fine line to walk between trash-talking your ex and telling your son the truth, but its his family too. He probably deserves to know what really happened, if not all the painful details.

Your son has to figure out his relationship with both of you, and it might be rough going for a while, but it'll be a lot rougher if he's dealing with made up stories or if he's making up things in his own head out of lack of information.

I bet ultimately he'll feel a lot safer and more secure if you can give him more of the real story.