How many second chances can you give a person???
I personally gave the most recent addicted person in my life two chances. The first time he betrayed me, I was shocked, dumbfounded, and severely hurt. We discussed it and decided that because we loved and cared about eachother so much, and because we were so compatible (clean and sober), that we would try again. The second time he betrayed me, I set my boundary. I told him if it happens again, we would not continue. It happened again, and I have honored myself and my feelings by sticking to my boundary. That person is no longer in my life.
I don't want to be married to a using alcoholic.
Then don't marry him. You are already aware of what you want and what you don't want for your life; so you're actually ahead of the game. Now you have to decide to honor yourself, bite the bullet, and move forward in your life seeking out what you DO want. Do not look back; that is not honoring yourself. Do not look side to side; that is second-guessing yourself.
What is the right thing to do here??
There is no right or wrong. You cannot look into the future and see what will happen or not happen. Let Go and Let God. Honor yourself and know strongly what you want for yourself. And then, just do it.