The speaker is trying to forget someone they once loved, and finding it painful. The first eight lines are a run of questions. Is it really so easy to lose a face once you know it so well? Is it fair that the light this person brought, which once gave the speaker hope, should be taken away? The speaker also remembers that their shared time made sorrow easier to bear, so forgetting feels like giving up something that was theirs.
In the last six lines the tone shifts from asking to deciding. The speaker agrees to overlook the beloved's likeness, even though it is beautiful, and asks to see it as something old and faded so that leaving becomes possible. The closing line gives the title its meaning: ending this glorious bond is hard, but letting the other person go is the right thing to do. The mood is wistful and quietly resigned, with sadness held in check by a sense of duty.