I am sorry to hear about your bad news. I wonder why he wasn't more encouraging? I understand that he needs to be truthful, but there needs to be some hope in your situation.
I agree with you, a second opinion from your GP is a good idea. Maybe even another specialist is a good idea. Doctors can be wrong just like anyone else.
People in therapy often feel that the therapist holds a lot of power. It can feel that way because the therapist seems to know all the answers. And when you are in therapy, you can feel vulnerable. But she is there is help you and guide you. If she is a good therapist, she will have no desire to how any kind of power over you, but instead will want to be a helper to you. It is quite common for a person in therapy to transfer some of their feelings onto the therapist. So if you feel powerless, feeling that the therapist has power over you and your feelings will be natural for you.
It would be very helpful to let your therapist know this. She will know it's transference and be able to help find the source of why you feel this way. Then you can resolve it from there.
Try not to see what happened to you as a big overwhelming thing. Seeing the whole picture at once can feel like too much. Try thinking about it in a different way. For example, change your thoughts to "I went through some very bad things, but I have help now, I am healthy and getting better all the time". When the bad thoughts start, try switching them to more positive thoughts. It will take the edge off how you feel because your feelings will follow your thoughts.
I hope you got some good sleep! Talk to you soon,