You question if you should stay and be a support. Didn't he have 3 1/2 years to utilize his support from you? And yet here you are, dealing with yet another of his relapses.
The question you have to ask yourself is, does being with him help me to grow both emotionally and spiritually? Will he be able to support me on those levels for the rest of our lives? If the answer is no, then you know what you should do.
I wish you the best!