I’m so sorry that you were hurt so much by people you thought were friends. I’m sure that makes trying again very difficult. I’m glad you are in counseling to take a look at what maybe you can learn from the experience. You do have understandable issues around trust. I hope you are working those issues through with your counselor.
As for your question: Of course it’s possible to make friends once you leave school. In fact, most people leave the area where they went to school and have to start over. You won’t be at all alone in that. Wherever you find a job, there will likely be other people your age who are similarly looking for new friends.
The good news is that you have lots of interests that will help you connect with others. I suggest you think about getting involved in an environmental cause or join a recreational league in a sport you enjoy. Those are promising places to start.
To get ready, take full advantage of the therapy you have now. Be open with your therapist and be willing to try new things. You are clearly an intelligent guy. It may be difficult but my sense from your letter is you have what it takes to make important changes.
I wish you well.