She may know it but she still has hope.......she's not willing to let go. The more you stay with her and be her shoulder to cry on , the more in the friends zone you will be. She needs to find herself a female best friend to help her work through this. That means you need to tell her that you can't be with her until she gets over him. If you want this to change you are going to have to let her go for now. You being with her is making her realize what's she's been missing with him. It's doing more harm to your chances than you thing. Remember nice guys finish last.
If you stay with her and be her support system, there will be a day when she shocks you and tells you she met someone else. You are going to be worse off more than ever.