Thank you for writing. I have a guess that it wasn’t easy to lay out all of your troubles so starkly. It must be very, very painful to live with so many doubts about yourself and the woman you love. I don’t blame you for being angry and sad. I give you lots of credit for not getting married until you settle at least some of these issues. No, you shouldn’t cheat to keep things even. That would set a divorce in motion before you were even married. You should get some help that will get to the root of the problem.
You describe symptoms that are consistent with a number of different diagnoses. Without talking to you, I can’t narrow it down. What I can do is suggest to you that you make an appointment with a psychologist for a thorough evaluation. You’re a complicated guy. You want to find a psychologist who has the skills to do some psychological testing if she or he deems it necessary to go beyond the usual interview in order to understand you. Ask you doctor for a referral or contact your local community mental health center.
I think you will find that naming your problems will give you some relief. Once you know what you are dealing with, you and the therapist will be able to develop a plan of action that will help settle your anxiety and build your skills for dealing with the social world.
I wish you well.