Letterman is a tool. Goes on the air after he finds out he is going to be exposed and admits "he made mistakes and is sorry" Dick would not have said a word if that guy was not going to tell the world about his indiscretions, thing is he got caught thats all. He would still be doing the same thing if he was not so sloppy and careless in his cheating.
Would you brag about cheating?
Would you go on television nightly, and say "Hey, I just nailed the young intern over there...Bob, you wanna put her on camera really quick?"
I haven't seen what his wife's response has been (if any), but it took her and Dave quite awhile just to marry, maybe they have an arrangement, and if that's the case, what business is it of anybody's?
Lastly, Dave did not say anything about his indiscretions because it was the girls wishes just as much as his to keep it quiet. He mentioned this on the show as he confessed.
There's many ways to look at a situation, it's not always a black and white, clear cut case.