The act of betrayal hurts because it is usually committed by someone you have trusted and loved the most. And you have been betrayed, your heart gorged. I just want you to know that you have the right to be angry and hold your grudge against that person and there is nothing wrong with that. Even negative emotions make you human.
However, you have to remember that not all people, in general, are like her. Not all will treat you the way she did, or they did; not everyone will treat you badly, the way you don't deserve.
Most people are cruel, yes, but some are kind and genuine. They maybe few, but they exist. You can expect that they will regard you correctly, because they know, as a human being, you deserve that. They will show you your importance, because you are important. In case you have forgotten, they will remind you. In case you have lost it, they will help you find it again.
In times of need, expect that they will choose you over anything else. Meetings. Classes. Birthday celebrations. Whatever. You are worth more than those. They know that you deserve to be the choice and not just an option.
Do not be afraid to trust again. Fully and genuinely. Opening oneself and giving in once more isn't easy, especially in your case, but you have to try. You have to try overcoming those obstacles and letting not the past defeat you. Not everyone you'll meet will stab you at the back, the way she did.
There are people who can and will show you your importance. They may be few, but they exist. I hope you find them. And I hope you find your fulfillment as a human being and the core of your existence. I hope you can say in the end, not matter how ugly and cruel the world is, that life's worth it.
I hope all these for you.
Sincerely.
To the scent of rain on dry Earth.