Therapy. You won't get there without it. All the self-help books, support from friends, or random advice from strangers on the internet won't help without therapy. If you have a bad history with sex, then you absolutely need professional help to explore the issues that are specific to your own life.
Anything short of therapy will be "most common problems" or "best guess" or "one size fits all" advice. Only a therapist can help you get to the core of what's specifically bothering you and show you how to deal with your own personal demons.
Preferably one who specializes in sexual trauma.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker