*EDITED* Best friend cheated on her boyfriend...

So my best friend recently told me that she cheated on her boyfriend of almost 2 years, but the way she brought it up makes me think this wasn't the only time. She told me "is it considered cheating if we sext daily, exchange nudes and go on skype after *boyfriend* goes to sleep? But we've never fucked" I was honestly really shocked. I said if you need to hide it from him then yes it's cheating. Then she just went "oh..." An hour later she brought up wanting to take a road trip during spring break to Georgia (of all places, right?) to apparently meet this guy and sleep with him. Multiple times we've been talking about him then her boyfriend will show up and she'll freak out and say "stop talking about it!" Then change the subject. I honestly think it's extremely childish and petty considering we're both in our 20's. It's going against my morals of not telling him, but if I did then she would never talk to me again. I feel so bad because he pays everything for her, and buys her everything she wants even when money is tight. She doesn't work, or go to school, sleeps all day until he gets home from work then bitches at him over the littlest things. She's taking advantage of him and it's killing me because he's so nice but a total pushover, just like I am. I need some advice ladies, please. This has been eating away at me for weeks since she told me. 
EDIT: Thank you for all of the input ladies. At first I was going to keep quiet to avoid the confrontation and be a good friend to my best friend who I've known forever, but then I started to think more and the past year or so she hasn't been a very good friend or even a good person to me. I realized that the other night when she pulled me off to the side and got mad at ME for going through my laptop (she went through my Facebook, Instagram and Twitter) because I accidentally left it open before I went to sleep. She was livid that I was talking about this situation to my other best friend in private (who she doesn't know) because I wanted more advice. Then she confessed later that the real reason she went on my laptop was to find something she could blackmail me with if I threatened to tell her boyfriend and she begged me not to tell anyways. At that point I pretty much said screw this bitch and left. I texted the guy she cheated on her boyfriend with for proof and screenshots of her actions and sent it to her boyfriend in a very long text message. I haven't talked to her since and as far as I know they broke up and she's homeless living at a friend's house. It didn't feel good to do but at some point enough is just enough.