Question about a situation

Ok so I don't want to tell a big story but I will give you the basics. My work is a warehouse and offices together for the same company. I work in the warehouse part.

So there is this girl that I like and she works in the office. She will come out to the warehouse for certain things through out the day. I normally do speak to her to say good morning , but it's never really gone farther than that. She seems to be a very decent person not trashy or anything and is kind of shy and very quiet. How ever there is this one guy that she always speaks to and you can tell her face lights up when she see's him and is always smiling at him and talking to him. If that is what was bothering me though I wouldn't be writing this post.

You see this particular guy is a real no count. He walks around the warehouse nearly everyday and brags about girls he's been that he's paid to have sex with. He has on several occasions walked up to me and showed me porn on his phone in the past. He smokes a lot of pot and sometimes comes to work with alcohol on his breath from the night before. He is married with 2 kids with his current wife and has at least one other with a different woman. Specifically said to me that he is going to try and "fuck" her when she first started working there. I could go on more about this guy but I think you will get the point.

The question is when I see him talking to her etc. I know what the deal is and it really pisses me off. I have came very close to telling this girl who the real him is and that he is nothing but trouble. Then again she is a grown woman she should be able to figure that out for herself. I also for got to mention he is in his 50s and she is around 27. What do you guys and girls think? Should I tell the girl the truth? Should I just let it go? Or am I just jealous? I don't know but I do know that every thing I have said about this man is fact. I do know that.