I'd say you are entitled to your feelings and I can totally understand feeling responsible for him, cause he has made it that way. Boy, this must be so difficult for you to accept, but it's not like you've been married 30 years and this happened! Where are his family and/or friends. I seriously don't think this should fall entirely on your shoulders, but I can understand HOW DIFFICULT it might feel to extricate yourself.

How about coming up with a plan for YOUR future?
1. Hire someone to help with his recovery.
2. Set aside time DAILY for you and you alone.
3. Start a journal about your relationship with him. Keep detailed records of your thoughts, feelings and how you are being treated by him, REGARDLESS of whatever medications he is taking, he should be treating you properly.
4. Set a date to make a decision about if you will marry him. If the date comes and you haven't decided, You can extend it if you like, just let yourself know that YOU and only YOU have control of your future.
5. Tell yourself daily that you are NOT a bad person should you choose to walk away. Hopefully, you will soon believe the TRUTH in that statement.

Hope this is of some help, you really do have my condolences.