he has to go from time to time otherwise she gets weepy and starts telling all of our friends what a dreadful person he is.
Think about what you said right there. Why does he have to go? If he isn't involved with her then he doesn't HAVE to do anything. Sounds like there is some emotional blackmail going on between all three of you.
It doesn't sound like a healthy relationship, frankly. You said in the intro to your blog piece "Please tell me how I can make this better and more amusing." Then you reveal in intimate conversation studded with snide remarks. I think perhaps you three deserve each other.
Don't be a doormat. If he's involved with both of you now, he'll probably do it again, even if you insist that he choose she or you. If he finds out you've posted the conversation you're toast anyway, so maybe ending it while the ending is good would be your best bet.