You are a man in anguish. That does not make you psychotic. I wish there was something I could say to help you stop worrying about what everyone else thinks and start taking care of yourself.
Twin relationships can be joyful but they also can be terribly complicated, especially when the personalities are more different than appearances. Sometimes twins unconsciously develop opposite ways of being in the world just to have their own identities. It’s the obvious solution. It certainly makes the point that the two people are different. But sometimes people take it too far. They don’t do this on purpose. It just happens. There are more subtle and more satisfying ways to be your own self than to be a mirror image of your brother. I think you need help finding them.
The way out of this is to see a therapist. I hope you can reconsider it. Yes, we therapists do see people with significant mental illness. But we also see people who are the “worried well” — people who are not mentally ill but who are troubled and who need the objective eyes and the information and support we can offer. You fit into that group. I am concerned that if you continue to withdraw and spin around and around in the same tortured thoughts, you will become ever more depressed. You need someone to help you break through the spin and start you on a path toward healthy self-discovery.
I wish you well.