She's just hurting dude. She's probably still in love with her last boyfriend. She's taking it out the cheap the way ---- flings. Don't get in the path of her destruction. However, she may appreciate you for life if you talk to her about her ex, and how she is acting now. She is using boys to make her feel her worth again. I say, ask her how she is feeling from her boyfriend. She will probably say, "okay"
I have a quote from the movie, "The Thomas Crown Affair:"
"Yeah, I was okay once, too. I ****ed five girls in three days, and flipped my car on the on-ramp."
She is probably in denial. Help her out of it. (If you want to sacrifice the time and energy and possibly even emotions.) Otherwise, MOVE ON.
Stay strong my brother,
"I still find each day too short for all the thoughts I want to think, all the walks I want to take, all the books I want to read, and all the friends I want to see."
- John Burroughs