I can relate to this. When I first found out about my wife's affair, it was the infidelity itself that tore at me -- especially the sex. I was told at the time that, in time, the sex wouldn't even bother me as much as the DECEIT and the DISRESPECT would. I highly doubted that.
It was true.
To have the woman you love look you RIGHT IN THE EYE and just sit there and LIE to you hurt more than anything. Knowing where they were going when they were going out, and the total DISRESPECT that that entailed.
You are much better that I (as usual) at putting these feelings into words.
When W moved out, I told her that I had hoped she had enough respect for me and our M to wait until the D was final before continuing her physical R with OM. She promised to do so, but we know how much that promise was worth. Imagining the sex hurts, but you are right -- the deceit cuts much deeper.
Me45 W35 M6 T8 D16 SD11 D0 Dec 07: Bomb July 08: Busted! Thread