Trust your gut, it is usually right.
You have a child, so the stakes are higher.
At this time, I believe that you are better off being a fiance rather than a wife. There are
far fewer legal issues to sort out if it doesn't work.
Once an addict always an addict, it is just a matter if they are activily using or not. And, relapse may always be on the horizon, one never knows when or if it will happen.
I wouldn't go forward with marriage at this time, there is no rush, your priorty is your child, you are his today and tomorrow, he is depending on you to make the right decision for him.
You are on the right track, keep going, think with your head not your heart!
Dolly