Welcome, Adeline. We call people like you double winners...those in recovery for substance abuse AND codependency at the same time. We have several members here like that who have done very well at turning their lives around.
Take a good read around, especially the sticky posts at the top of the forum. Also, there is a wonderful book called Codependent No More by Melody Beattie that has helped many of us figure out how we got this way and how we can live healthier lives by making a few changes in our thinking.
I'm not sure how long your fiance is in prison for, but it is a good thing that you are taking care of your own addiction and issues right now, so that when he gets out you can decide on the healthiest path to follow.
Good luck to both of you in your sobriety.