Dickinson uses precise geometric language: citadel (fortified structure), undermined (dug beneath), bisected (cut in half). She's treating emotions like engineering problems. Childhood grief "threatened" and "undermined" like a siege, but adult grief simply bisects—divides what you thought was whole.
The key word is bleaker. Not "bigger" or "worse"—bleaker. Adult griefs are colorless, empty, unfixable. They make childhood sorrows look "sleek" (smooth, manageable) and "easy to repair." The poem's insight: we don't outgrow pain, we just encounter pain that can't be fixed.
Consummate means complete, perfect. Time doesn't just soften memory—it upholsters it perfectly. The metaphor suggests something almost luxurious about distance from childhood pain, which sets up the poem's bitter envy in the final lines.