Yeah, you have to do no contact right now.
And yes, you are the plan B right now. With you constantly talking to her and trying to tug her back into a broken relationship, she's just going to pull away. She's doing all these nice things and saying all these sweet things because she wants you to catch her when she falls, when this other relationship she has fizzles out. Don't be that cushion.
It's feeding her ego by contacting her and it's also reaffirming that her decision to leave you was right. All the desparation on your part is portraying this constant need, and neediness is not attractive as we all know. I know you feel guilty and feel like this is your fault for getting too satisfied and comfortable. It's a common mistake, I was guilty of it as well. It took me really losing my girlfriend and a few months on my own to really become a whole new person, to get my priorities in line and so on. Falling off the face of the earth to her right now and being away for some time is the only way that you can really "change" in her eyes. And it will cause her to miss you, if she still has feelings for you. If she contacts you, I think you should flip this upside down and tell her that YOU need space and that she should respect that.
Is it possible she will find somebody else? Yes. Is is possible that another person can replace you? Yes. Is it likely? No. Do not be afraid because if it doesn't ultimately work out with her, it will with somebody else. Don't try and drag her back into your old broken relationship, take some time out for you and work on yourself and than maybe if it works out you guys can try and start something new in the future. Right now it's too soon.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.