<human>: Can you provide a brief rundown of the text in within 3 sentences?

Hi.. I did a bad thing earlier (snooped on BF) and now I'm paying for it. I caught messages between him a female coworker... This is the same coworker that he has avoided telling me about in the past. Ex: He went to the movies with her, his brother, and possibly a male cousin of his. I only found out about this when his SIL posted a status on FB 
tagging them in it.

So anyways, I'm borrowing my boyfriend's old phone at the moment since mine broke earlier today. A lot of his stuff is still signed in, including FB for some reason, so I got curious. I logged out of it after a message or two (honestly). 

As awful as it sounds, I'm pissed at myself for not reading more. I kind of freaked out and closed out of it automatically. 

I normally have more trust in him, I'm not sure what was going through my mind :( I wouldn't care about this usually but it's just that he works with this girl all day, hangs out with her sometimes, but still tries to avoid saying anything about her to me.

Am I upset for no reason? I feel like I have some reason to be upset but I don't know how to talk to him about this.. Should I just pretend it never happened and try to forget about it?
<bot>: Did a shitty thing and snooped on BF, found him talking to female coworker he always says/acts like he has nothing to do with (even though they hang out outside of work).