I think it IS never-ending.

I wonder if you would think it selfish and feel guilty if your having to go into "no contact" was due to say, a flare of MS tremor? Why think any differently for your own concerns?

What good does it do ANYone if you are unable to function?

IMO your family is still running on their family dynamics. You, however, have pulled out of that rulebook. They do move in on you because it's ingrained that they find a scapegoat, attack the weak, accuse someone because someone has to be at fault and made to do better...etc etc etc. They haven't changed, you have.

The reason you haven't had to be on constant vigilance is because YOU have kept your boundaries intact...far enough out that you didn't feel like hypervigilance...though maybe it still is? Just more comfortable?

Go back to what works. You might need to adjust it a bit from time to time, but I doubt it's necessity ever goes away.

Just my POV.