Relief, tj.
Only relief.
But that's when you know, you are sure, you have gotten past the denial and the enabling and the attempting-to-fix-and-rescue, you are aware that the situation is hopeless as long as the N wishes to remain an N and that it's only they who can change it... and they prefer it just the way it is.
That's when all the mourning has been done previously and toxic hope has been laid to rest. There aren't any more 'hooks' in your skin [I shoulda been more this, less that, I could have fixed this if only I had done such and such, etc. etc.]. You know it wasn't about you. You know it was there long before you ever were, and would remain whether or not you were present or absent, no matter what you did or didn't do, or how long you did or didn't do it.
Then - only relief.
No guilt mixed in with it, because you know you did all you could, and more than most other people ever would, and nothing would have been enough, nothing could be enough ever.
No shame or blame mixed in with it, because you know you were not the inadequate one.
Just relief. For them as well as yourself, because you also know just what a wretched, blighted, empty life they really had, and their suffering has ended at last.