Describing what love feels like, or is, is one of the main gestures of this poem. With no specific setting to hold on to, and no particular speaker to get to know, the images of his concept of love become the only things to cling to in the shifting landscape of our speaker's thoughts and emotions.
Lines 7- 8: This straightforward, though strange, simile, compares the speaker's brother's love to spilled water running back to its container. It's straightforward in the sense that it says A is like B. The comparison itself, though, (identifying how they are alike) is not straightforward, and lends the simile some mystery and complexity. How can water run back into its vessel once it's spilled?
Lines 7, 16, 27: These similes also make a refrain that repeats throughout the poem, with all three beginning "His love for me feels [or "is," in the case of line 16] like…"
Lines 18-19: The second love simile goes on longer than the other two. In fact, it carries over into a second sentence: "But the needle pierces…" What's so nifty about this technique is that it makes the father's sewing no longer seem like just the descriptive part of a simile, but also a fully realized image, like, say, a memory.