Wanted to respond sooner but you know life gets in the way of the forums and had to put this together a minute here, 5 there - style. Which always makes for a disjointed, ramble...
I see that ALOT. So much, in so many areas. I've seen one of my children, over the years, attempting to break free of the repetitive mania cycle. As soon as he looks like he is going to implement some of the many techniques he's been shown, he will stop and "but wait, before I do (game changer), first let me..." which we learned, of course is some sort of delaying tactic or a touching-one-last-time of the old, unhealthy-but-comfortable thing/lifestyle/thinking process/drug - whatever it is they are trying to change.
You get to the point, I'm sure you've experienced yourself, when someone you know is going to come off the wagon or a have a significant regression of some sort. Its when they have made progress, begun to see positive things as a result of implementing techniques or they've been attending their AA/NA meetings regularly, telling everyone excitedly how well they've been doing, starting to preach the message - I think you even mentioned your husband getting to this point - and right as they reach that moment ... its almost as if they've reached a true crossroads within themselves; there's a moment of suspended animation when they are between worlds and they are truly free ... free to make a choice. They reach back.

But it seems like there are setbacks from human weakness that are too powerful to overcome at that moment and require redoubled efforts - like an army being repelled again and again from taking some objective where the overall intent to win the war is there - but then there is a kind of, I dunno - picture someone struggling to help their friend scale a rocky precipice that they've gone over, struggling through tears, exhaustion, near-slips for what must seem like an eternity to get the victim to safety - and just as he's right at the point where he's made it, he looks up at his helper's dirt-stained but joyful face, and with a smirk, just lets go of their hand.

"What?? Was that for my benefit?!? You're so hateful that you consider yourself an expendable casualty just so you can deliver the ultimate ____ you!?!" The additive summation of all those relationship-sabotaging choices made over the years having that net effect, maybe.

Just enough; just a taste. Like sitting down for a mouthwatering meal and after a couple of succulent bites, the serveuse whisks your plate away, wagging her finger "No,no,no. That'll do."
Ja, those fleeting moments keep us hanging on, don't they? We live for them. I read something once...can't remember what it was about or pertained to...but the gist of it being that after a certain point in adulthood is reached, we will spend the rest of our lives trying to get back to that point where we thought we were at our best, when we were at our pinnacle.

Maybe some of us spend our lives trying desperately to recreate the moment when our SO was at their best.
Yeah, there could be some aspects ... I've heard my son's mum, for example, say "I'm so afraid for him, afraid for his future", and I've said and felt this myself (which is why I'm on this forum). The implication being his life will go on without us and its our job to make sure he's ready. When I've worried about my spouse or she's had fears for what would happen to me, its more 'I'm so scared for him/her and our future.

*I thought I could {inspire} him {to make} the life that no one else thought he could have.*

I can't say, maybe - but I can also see where the storms and realities of life can blur lines and boundaries and you can end up assuming roles that you never intended to. It just has a way of creeping up on us, bit by bit, until one day, you step back and "how did it come to this?!?"

Did you ever see the film, As Good As It Gets?

"...because you make me wanna be a better man."

You did. And someone very much like you inspired me to want to be a better man; however, the burden - work, effort, struggle - of being that better person lies with us and us alone.

That's a very lonely place to be, I know. It feels like there's nothing. Nothing. The time I was there, never so helpless. It was also the time I was never so amenable to change, receptive to game-changing ideas, breaking negative, defeatist habits (mostly of thought) and associations that would have been near impossible before. You're potentially as close to being able to be re-wired as you will ever be as an adult.

This phoenix can rise from the ashes.
Now, that's the best thing you've said. Great beginning to better thing to come. See your therapist once a week, find a second and see them on alternate days and then find a third one and put them on a retainer - just to make sure the other two are doing their jobs.
Hits too close. Another confluence, maybe.

Yes, it does!