The speaker has come to the end of a relationship, and the poem is careful about what exactly has run out. "I am out of love / but only ours": the feeling that has gone is the shared one, not love in general. That small correction makes the loss sound precise and a little rueful.
The rest of the poem piles on other kinds of emptiness. The speaker is "out of doors" and "poor," which could mean literally homeless and broke, or simply shut out of a life they once had. The title, "Down and out," fits either reading. The strange line "makes the morning a noon" suggests time has been thrown off, as if the day arrives too fast or too bare, with no gentle start.
The ending is quiet and unresolved. The speaker "will shut my mind," which sounds like a way of coping: closing off thought to get through. The mood is bleak but restrained, spare and tired rather than angry, and the poem simply stops, leaving that decision hanging.