I was mortified when my mom came to visit and saw the extent of my ex's drinking. When I was living with it, I did so much minimizing and denying to myself that it took someone from outside the situation seeing it to jolt me out of my rut of depression and resignation.
Why do you fear others finding out about the extent of his problem? I think it's because you know the right thing and fear is holding you back. That's what's keeping you in this relationship. Fear, not love.
When I finally left I realized that I didn't love my ex and hadn't for a long time. I was just so worn down and defeated that I felt paralyzed. The universe is trying to tell you something. I would listen. This gets so much worse. If you think the future of your relationship depends on him getting help, then you are in the wrong relationship.