The speaker is an insomniac, but the poem treats sleep less as something to be won than as an unpredictable visitor. Sleep comes "but not on purpose," as if it drifts in by accident, and the comparison to a swan makes it feel wild and indifferent. Neither sleep nor the swan understands "being civil": they don't answer to our wishes or follow our rules, however much we want them to.
The last four lines turn more sorrowful. Drawing "the last rose" to fill "the hole in my heart" suggests a small, almost ritual attempt at comfort, perhaps a card or an image, though the poem doesn't say. It can't really fix the loss. The speaker then goes home to bed "in a broken country," which could be read literally or as a way of describing an inner or shared sense of damage. The mood is quiet, tired and bruised, with a thread of dry wit. Rest is uncertain, and so is comfort.