In this poem, two former sweethearts from Ohio (Bill and Mary) randomly run into each other again in Washington Square in NYC one night. We learn that they did not marry because:
Then something not very important had come between them, and they didn’t speak. Impulsively, she had married a man she thought she loved. Bill went away, bitter about women.
When they meet, Bill notices that Mary looks very old. She notices that he does not look old. They are awkward and catch each other up on their lives. Bill is a lawyer and has two children. Mary is married, works at Columbia, and has three children. Mary seems unhappy and unfulfilled.
She understood. Under the trees in Washington Square, she found herself desperately reaching back into the past. She had been older than he then in Ohio. Now she was not young at all. Bill was still young.
They invite each other to visit, but neither is serious. Mary's bus arrives, she boards the bus, and then desperately tries to say goodbye to Bill. She remembers that they did not exchange addresses or phone numbers. And she regrets forgetting to tell him that one of her sons is named Bill. She shows regret for their lost relationship, but he does not seem to feel the same way. All he notices about her is that she looks old.
It appears that Mary was the one that broke of their engagement years ago, leaving Bill bitter against women. But at the end of the story, it appears that Mary may now be the bitter one -- or at least the one with more regrets.
Read about Langston Hughes here on enotes. He was also noted for his poetry and is part of the Harlem Renaissance. Many of his poems and short stories deal with lost love, lost dreams, etc.