One of my parents did. It hurt at the time, but on a grander scale I think things are much better in my family now because it became public knowledge, and because my parents are no longer together. I'm not going to go into detail as I don't think its fair on them, but the other parent had been aware of it for a long time. It showed around family events, Christmas, birthdays and the like.
These days all of us can get together in the summer and really have an enjoyable time as a family. In many ways things are better now than when they were together. So my point here is things can and will improve.
Both of them are still your parents though, and being unfaithful doesn't change that. It is important (and perhaps difficult) to realise that it can happen for many reasons. It rarely happens just for the sake of it, their is usually a chain of events that leads to it happening.
It will obviously hurt because it is two people you care a great deal about, who have raised you. But they are also people, and people do make mistakes. Error is human nature. It is important that you allow them to deal with the aftermath, and do not take sides. They are after all both your parents, and emotions will not help if you take one side or the other. You may never also know the full extent of what led to it happening, and you need to take this into account.
It is okay to have strong feelings regarding cheating. Some people have very strong views, others do not mind so much, while others may not even be bothered by it.
