Please help, I can't lose this girl!?

I've been talking to this girl for about two months, and things have been great. We started talking not soon after she broke up with her ex, who cheated on her, that she dated for two and a half years. There have also been other times in the past two months that he's said offensive things to her. Last night she got a text from him saying that he wants her back and that he still loves her and wants to marry her. She said no and for some reason that she doesn't know she feels depressed. I want to help in any way I can. What can i do?