<human>: Can you condense the text into three sentences or less?

I've been dating this girl for about a month, and things are going great, but last night she showed me a whole series of Facebook private messages from one of our coworkers, who is the age of both of us combined. The messages were mostly harmless, except that she's receiving several of them each day. The coworker is using a fake Facebook account, likely so his wife doesn't find out. 

I have felt sick to my stomache since she showed me these messages. Every morning, it's things like...
-Good morning
-Why are you ignoring me?
-Did I make you mad or something? 
-Please respond
...and it goes on, and on, and on, even though she's never responded to a message. 

I'm truly worried for her safety; I don't want to seem like an overly-jealous boyfriend or anything, I just want to make sure this doesn't escalate. I'd like to get him fired, but she asked me not to tell anyone she showed me those messages. What can I do? Rather, what should I do? As much as I don't want to lose her, I want to keep her safe from this sexual predator.

"Whoa, sexual predator you say? Those messages sounded pretty harmless." Well, in addition to these Facebook messages, she's told me other things he's said to her (and other girls) at work. For example, he's always talking about other coworkers' boobs, butts, and so on (some of these things I've witnessed myself), and he said he'd like to see her naked. You may think I'm overreacting, but this guy is a serious fucking creep, and he makes my girlfriend, as well as several other female coworkers, very uncomfortable.
<bot>: Coworker using fake Facebook account to harrass my girlfriend, and I want to get him fired, but she doesn't want me to tell anyone about what she showed me.