If he's seeing somebody else, then this all makes more sense. Unfortunately, asking if there is somebody else usually doesn't work. Sometimes it does, but usually people having an affair lie about it.
That's where gathering intel helps. If you knew who he was having an affair with, then you could attempt to bust the affair before you let him go. As things stand, I am really at a loss here.
Take good care of yourself, and start making plans for yourself.
M-47,W-40,No kids D-filed 5/27/2010 Piecing - 10/21/2010 -=Soon to be banned=-