The posuk at the beginning of Megillas Eichah states, “Alas, she sits in solitude! The city that was great with people has become like a widow.”
The Bais Hamikdosh was destroyed and Yirmiyahu Hanovi lamented that the great city of Yerushalayim is all alone. He compares it to a widow who, unfortunately, must also stand alone, without the companionship of her beloved husband. Yerushalayim stands alone, without Klal Yisroel filling its streets with the sounds of life and the service of Hashem.