It's absolutely riveting. I have no idea how far we are from crescendo, but I'll say here that I love the title. It's so hard to pick a title that conveys something succinct and important about the work, but 'Thorn Forest' is just dread. And that's what I've had from the first stanza - dread and sympathy.
Where we are now in the story is a place between dread and sympathy, a kind of pulling, inexorable, toward the cliff's edge. You can see it happening, diagram it back to the whys - at least for Jacob and Anna - and there's not one damn thing that can put the brakes on it.
For me, that's what you've captured so far.