Is asking a stranger online to send a pic cheating?

I found out my husband was online one night and started saying hi to a couple of girls the asked one to send him a picture. He says he doesnt even remember doing it he must have been drunk. He yelled at me for not trusting him about something so stupid but isnt this looking for something outside of the marraige? One time I also saw he was on casual encounters on craigslist but I cant prove it because we had company earlier in the week and he swears it was them. Am I justified in being upset or is this really nothing?