What do you want for yourself that you are asking this question?
Are you looking for someone stable to build a life with or do you want someone who needs fixing so you can feel needed?
Has he done some noble and responsible thing for you in the past that you feel compelled to hang in there with him?
I can't really give you any advice on this one. If you have not yet answered for yourself why you are with someone who breaks your heart, your finances and your spirit, then even if you leave you'll either return to him anyway or find someone just like this person.
Ask yourself if some other woman who you truly admire as self-confident and in control of her life would be with this person. What is your life likely to be like if he does decide to stick with rehab, if he does not stick with it or if he relapses off and on for the time you are with him.
You don't have to hate him, but maybe ask yourself what you really want and if he's the guy you want to save.
Hope is one thing (and a good thing), so there is always hope. Maybe a more practical question is - how much are you investing and at what point do you want to cut your losses?
Relationships can be very sentimental, but you still have to pay the bills and I assume you want some type of quality of life. So, some practical questions are also helpful.
Hoping you find the clarity you need.