How can I make it stop??

Last month, I wrote that I was going into mediation very scared. As it turned out, it was okay because I had both my attorney and the mediator as a buffer. Because my ex didn't feel like he got what he wanted, though, he asked that we schedule another mediation. This week I cancelled it (3 weeks notice). Not only do I now have a conflict, but I think it's premature because he hasn't actually tried anything he says won't work for him.

Because I cancelled mediation, he's threatening to take me to court for breach of contract, contempt of my decree, etc. He gets married in less than a week and his rage at me is compounding my the day. Why? I try not responding to him, but then he simply overrides me (he re-instated the mediation session because he didn't feel my excuse was adequate). I try responding to him reasonably and he acts like I've called him every bad name in the book (which I never have...except for once when I called him an a**hole an anonymous blog he found out about -- and now I don't blog at all anymore because he threatened to sue me for defamation). I get even the slightest bit angry and he goes ballistic, as if I have no right to get angry at him, EVER. Meanwhile, he tramples our decree whenever he sees fit -- making unilateral decisions about the kids or, worse, letting his almost-new wife do it.

How can I starve him out??? How can I reduce contact without him suing me? At what point do his threats become enough to constitute harrassment? And, really, why is he so focused on extinguishing me the week before his wedding?

Any help would be appreciated. I'm so sad, so tired, and so beaten right now. And I hate it.