"You did the worst thing you could possible do to me," he said. "The worst thing, and you knew very well it was the worst thing, and you did it anyway. Which part of that am I going to want to think back on?"
"Oh, I'm so sorry," she said, weeping afresh. "I'm so sorry you can't see it the way I see it. I'm so sorry this happened."
"It didn't 'happen.' You did it. You f***ed the kind of evil s*** who would leave this on my desk for me to read."
"For God's sake, though, Walter, it was just sex."
"You let him read things about me you never would have let me read."
"Just stupid sex four years ago. What's that compared to our whole life?" (3.6.137)
It's a fair question, that last one. But is it the sex that Walter is most upset about and hurt by? One could make the argument that it's really the things <em>surrounding</em> the sex – the desire she felt for Richard, and her pursuit of that man's affection. But perhaps most of all, like Walter says, it's really upsetting that she would share this revealing document with Richard, and Walter would only read it once Richard had cruelly placed it on his desk. Ouch.