RedKennedy, you really shouldn't do it, but now it's done, just close the book on it and don't do it again.
My husband is a bugger for reading my email, looking at internet forums I post on... All of it. (DH if you're reading this; you are nicked!) It bugs the shit out of me becuase it's an invasion of privacy, but worse, he's occasionally found something he didn't like. More often than not, me complaining bitterly to my mates about him. Something we all do, that's fairly harmless, but taken out of context, it's really damaging.
I'm only saying it becuase the worst thing you can do now is be suspicious. You could end up getting caught for snooping and it's really not worth it. I had a boyfriend once who was in a band and I know you imagine things when they're away so I do understand where you're coming from.
I'd say you'd be pretty miffed if he did it to you though. I really, really think you should leave it. Don't dig, don't investigate and don't look again. Things taken out of context are dangerous.
Big hug because I know you feel bad about it. I'm not having a go, I'm just letting you know that whatever you saw, is highly unlikely to be the whole story so you mustn't judge. x