The speaker is making an effort, and the first line admits it: he "labors" to think of love. That word suggests it doesn't come easily. His mind keeps drifting toward darker things, "ash" and "the void of death," and he is trying to set those aside in favor of something warmer.
The poem then narrows into memory. He gives over thoughts of sex too, and what replaces them is oddly specific: "the door to the shop," and the first time he was with her. The image that closes the poem is a physical one, his eyes "drinking" in light until they are sore. That suggests a kind of overwhelmed devotion, looking at something so intensely it almost hurts.
The mood is quiet and a little aching. Love here isn't an easy comfort. It's a deliberate act, a way of pushing back against dread, and the title, "Blues," hints at the sadness running underneath. The final image is bright, but the speaker seems to be holding onto it.