Subarnarekha/The Golden Thread
From Worldcat: "Ishwar and his sister, Seeta, go to Calcutta to look for work. There, they meet the orphan, Abhiram, and take him into their family. Ishwar finds work at a steel mill and raises the two children there. When Seeta and Abhiram grow up, they fall in love, marry, and move into the city. Communication dwindles between Ishwar and the couple, so when Abhiram dies in an accident and Seeta turns to prostitution to survive, Ishwar has no idea what has happened until it is too late."