Having recently lost someone very very close to me, I know much of this poem. But an infant never born to bring all this wonder into the world. I've known that loss too. We don't lose what we had or what we did, and all that love still exists. When someone dies, or never lives, we lose the chances of the undone. Beautiful poem.
Loss of a loved one is always hard, but so is the loss of a potential loved one. The mind starts to wander and fill in the unknown, adding flavors that can never be tested. It is a heavy sadness.