Rutwad, I have never been in a situation like this. I don't know what to say to help. But I do know, from hard times I've had in the past(unrelated) that certain perspectives can be used in multiple situations. The first is, look at what you do have. You have family, friends, and health. Take hold and cherish these things. By not telling your parents, you are pushing them away. Not intentionally, but that's how they may see it if they find out after the fact. I know you may not want to tell them, not only because of the problems they may be dealing with themselves, but after telling them, they will try to see what they can do to help. Not only will they ponder on what they can do to help her see the error of her ways, but also, if they fail, what kind of advice they can give to consol, and counsel. If you don't want them to worry, assure them that you are doing all that can be done. You know your parents better then anyone. It'll come to you. Trust yourself. Next, realize that if she doesn't come back, it's for the better. As good as the best of friends may be, they would never do what she is doing. I know those who you love the most, have the ability to hurt you the most. Those who can control their own pain and frustrations have just defeated their own worst enemy. Behold the power of your own thoughts. You have the power to increase your own morale or drive it in the ground. You will become what you think of most. Think positive. Be positive. Don't loose focus on what's important. Although this is no game, and from what I've read, you still care for her, you need a strategy to plan out the time neccessary for you to get through this.
Trust is like a large glass vase. It takes skill, craftsmanship, planning, and execution to make it into a work of art. Yet once it's broken, all the glue, skill, and care can never put it back to the way it was. Your best friend has, for reasons known only to her, just broken a trust. It will never be the same. It's very wise of you to take care of you finances, but I too recommend counsel. If you didn't see this comming, there's much more you may not see comming. Good luck, and stay connected with us. We're here to help as much as we can. And it's worth repeating, stay positive.