I think he has something to hide?

Last night I stopped by my boyfriends house unannounced. I've been having some family issues recently so he was not upset by my surprise visit. Shortly after he invited me in he noticed that his email screen was up with a message open so he promptly went over to the computer and logged off that screen. I wanted to ask him why he was so prompt about logging out of his email but I was at his house unannounced and I felt that I didn't have the right to ask. Today I really want to ask him about it but he could say anything and I'm already upset about my family issues. Would you ask about it if you were me? My gut is telling me that he was hiding something. We havn't been getting along all that great lately and this just makes things worse. Should I confront him now or when I have a better handle on my emotions? If he does admit that he was hiding something that would be it for me I will be so done with him. I feel awful what should I do?