The whole poem is one word repeated: "owe." Three lines stack it up like a pile of bills, twelve times in a tidy, orderly grid. Then the last line starts to break. "OW" appears, then "OW" again, then a lone "O," and finally "WE" is left on its own at the end.
That splitting is the joke, and also the point. Say "owe" aloud and it sounds like "ow," the sound of pain. So debt and hurt blur together. The final "WE" adds another turn: the burden isn't just one person's, it's shared, or at least something "we" all carry.
The speaker's feeling is never stated, but the mood comes through in the shape. It begins numb and mechanical, like a ledger, then cracks into a wince. It's wry and a little bleak, though the playfulness keeps it from feeling heavy. Debt here is something you feel in the body.