Vosh,
I have just re-read all your posts and I can't get my head around how she is so completely disregarding you and your emotions in all this, why is she so desperate to get it on with this other person right now when she needs to be home with you working this out, it just doesn't make any sense.
If she had any feeling and/or respect for you and your relationship left she should have stopped at the door on her way out, turned around and sorted this out.
Sorry to say it but this looks like its all over rover from her side, and I sure could not do what you are doing right now.
Stay Strong, you are the better person in all this.