How can you tell if your spouse is unfaithful to you?

I think you can start to tell depending on how they act towards you. If there is a sudden change in behavior, whether positive or negative, I think it indicates that something isn't right. It doesn't necessarily mean they're cheating, but more often then not, once someone finds out their partner has been cheating, they can tell you after the fact that they have been noticing a difference in their behavior lately. For example, if they are real stand-offish It might be because they are feeling guilty and don't feel right about it. On the other hand they could be ten times nicer to you because they know they're cheating and feel guilty about it.