I know this response is coming out of order as I'm just through reading a few posts, but in case I run out of time tonight I had to post a few quick thoughts...I'm sure the others picked up on this too.
KAW I really don't think CAW planned to have the OM there when you were expected to show up. Wouldn't just "popping in" be consistent with the kind of "man" he is?
The way you decribed her behaviour when you came in screams this to me. Does that take away any of your ANGUISH at seeing the SOB there? No. But in your letter you assume that she planned it to hurt you and that just might not be the case at all.