Hey X,
Have you thought about how you want things to be and what your own boundaries are?
If you are the one giving him the campral, that sounds to me like he is not taking responsibility for his issue. As those can only work when they are taken, and do not address the issue to help put someone on the path to recovery.
It sounds to me like you are only seeing two options: marry and hang on, or leave. But, you have more than just those two options. For ex. choosing to delay your wedding until you feel more comfortable and strong in what you will and will not accept.