No, this was not a failure. This was a victory for YOU. Your partner was the one who failed — he failed you, he failed himself, he failed your partnership. Whether you believe it was his fault or that he couldn’t help himself, he did indeed fail you. You were right to leave.
I speak from personal experience. My ex was an opioid addict. I saw the signs as soon as he started sliding down that road, but couldn’t leave because I didn’t earn enough money to support myself.
Meanwhile, as I begged and pleaded with him to quit or at least get some kind of help, he alternatively promised to quit (and would sober up for a few days, but go right back to getting high), or simply tried to lie about it. He went through $50,000 in a year. He was utter chaos — either passed out (sometimes in the middle of conversations), ranting and raving like a lunatic, or crashing stupidly around the house, breaking things. He drove under the influence, though thankfully only got a ticket and didn’t kill someone. By the time I finally left him, there was nothing of the old Chris I fell in love with. It felt to me like I was chained to a zombie, being pulled down into the darkness with him.
If Al-Anon or Narc-Anon gives someone peace, then more power to them. But no one should be expected to stay with an addict, to sacrifice their sanity, their health, their homes and money. Leaving is the best thing you can do. We need a support group for that!