Hi ahoffman and a warm welcome to you from all the Staff and Moderators. It sounds like the nest was predated, but I don't know what by. Unfortunately it is very common, a high percentage of nests fail sadly and we don't usually know the reason. One (or both) of the adults could have died or been killed. Something could have predated the nest, usually to feed their own young. Or it could have been disturbance, so as you are worried it might have been something you did, maybe you've been looking in the nest box? If so it really is best to leave them alone.
I'm sure you will enjoy it here and I look forward to hearing your news.