I have a friend who went through a similar situation–they were engaged, she broke up with him and blamed him for a lot of stuff, then she got together with his longtime best friend. My friend wound up growing and learning a lot about himself.
However, I’d say that right now you are very much in the grieving part of it. No one has died, but it’s like a death, to have your girlfriend leave and your girlfriend and your best friend betraying your trust, and then leaving you out in the cold. It really hurts.
What I’d suggest is finding a grief counselor or therapist (if you don’t already have one), and let yourself feel the feelings. Don’t try to push them away or bury them. Let yourself safely grieve, if you can. There is nothing wrong with grief. There is nothing wrong with tears.
I know this may seem impossible, but try to focus on the present instead of obsessing. If the present moment hurts, grieve for it. Distracting in a positive way also may help: things like going for walks and looking at the environment around you and concentrating on the sounds, smells, feel.
It’s possible they may never come back to you. You don’t have control over that. The only thing you have control over is what you do with your feelings. They hurt, but as I said, they really should hurt. Being in pain, torn up on the inside, is a normal response to something like this.
Is there a peer support phone number in your area? Perhaps you could talk to someone about it sooner rather than later.