Friends with this girl who just broke up with her boyfriend

Okay here is the deal. Im friends with this girl who just broke up with her boyfriend . She first called me crying b/c she was so depressed but I help her get threw it all. A few days later she takes my advice and goes on a date to get her mind off of her ex. a week later she ends up dating this guy and I soon find out from some friends of mine that this guy that she’s seeing has a history of hurt all of his other girl friends after hes done with them. Now I dont want to tell her b/c she is happ..now but latley we have been hanging out and I can tell she is not happy b/c when ever he textes her or calls shes always thinkin about something and she starts to cry. I ask her whats wrong but she says nothing. Everyday I ask her if he has been treating her good and she says yes. This springbreak I went on a roadtrip with her and its was so awesome. We talked for 5 hours straight without any music on or anything. I could tell she was happy hanging with me…even when we got lost . Lolol but on the way home she was quit and I couldnt really tell too much b/c I was driving but it looked like she was crying. I ask her if everything is alright and she just looked away and said yes. …I soon saw that she was text her new boyfriend. I hung out with her two nights ago at her house and ended up leaving around 2 in the morning. All we were doing was watching movies and talkg. Well here is where I want some advice from a girls point of view. she kinda knows that I like her but I dont want to come on too strong. I love this girl and I would do anything for her and she knows that. The thing I want advice on is do you thing I should tell her what I know about her boyfriend. how he plays all these girls. I really love her and I know she is happy but she just got he heart broken and I dont want to she her cry again b/c I kills me inside. What the hell should I do.