I'm a newcomer to this board, and I wasn't going to post anything, but writerboy, your post really touched me.
I want to second Silenteardrops letter suggestion, especially the one about writing to your boy explaining to him what happened. I can picture that really helping him overcome some of the issues he's going to have to face when he grows up. Perhaps give a copy to a trusted friend or relative for safekeeping in case anything should ever happen to you before you can pass it on to your boy.
I think it's very insensitive and uncaring of your ex to bring her bf along with her when meeting you. You're going to be discussing personal issues, nothing to do with him. I'm sorry I can't offer much in the way of advice, but I can sympathise.
I hope you're feeling better.