The reason my husband kept this information from me was to spare my feelings. He has felt very guilty for doing what he did because he knew it would hurt me deeply. He figured that it was over and done, he can't change what happened and telling me to ease his guilt would only hurt me. He wanted to take the brunt of the guilt to spare my feelings.
Am I hurt by what he told me - absolutely! I'm heartbroken. Everytime I walk past that room - I think of them having sex. Really sucks to have that reminder everyday in your own house. About 7 months ago - the 3 of us had sex in our bed because we didn't have time to go to a hotel. I did struggle with this decision for a long time - but I wanted to surprise my husband and this is where we had to do it. For a few weeks after - I thought about that a lot with a mixture of excitement and regret. A few months later - we got a new mattress (not because of that - ours was really old) but it did help me to not constantly think about it. With time - the thought went away. I know that this too will go away eventually. Of course, that's the room I keep and wrap Christmas gifts in - that will be a wonderful thing to think of next Christmas.
Now - if he cheated on me and didn't tell me - I do consider that ommission lying because he would be doing it to protect himself. In this case - I realize he did it to protect me, not to protect himself.