Long-term
If the relationship were clearly bad, you'd leave. The problem is that it's not clearly bad. Every time you raise something, it improves slightly. Not fully, but enough that leaving feels like an overreaction. You've been almost about to leave for two years.
The game
She has calibrated, through a feedback loop rather than deliberate calculation, where the floor is. You signal dissatisfaction. She makes an adjustment. You stay. The adjustment doesn't need to address the underlying issue. It needs to get you back below the threshold where leaving feels justified.
Each round the information is local: this specific thing got better. The pattern (that the improvement always stops at the same point) is only visible across time.
The equilibrium
Each adjustment resets the clock. Your threshold drifts down as you normalize the baseline. The floor drifts with it. The relationship stays technically intact and progressively worse. Neither person decides this is happening. It assembles itself from iterated rounds of the same exchange.
The ratchet runs differently than in the Lifestyle Ratchet. There, the standard of living accretes upward and becomes hard to unwind. Here, your expectations ratchet down and the floor follows.
Dominated strategies
Responding positively to each individual adjustment. In isolation, any improvement is real. It's progress on the specific thing you raised. The dominated part is treating it as evidence the underlying problem is addressed.
The only move that changes the game is naming the pattern rather than the specific complaint. "You made an effort last month and it's gone again" is different information than any single grievance. It makes the shape of the problem visible instead of giving her a specific adjustment to make.