Why did Calypso tell Odysseus he could go free?
Calypso was the daughter of one of the Titans, and she was in love with Odysseus. He stayed with her for 7 years weeping and crying for his home. He still loved his own wife Penelope.
After a time Zeus sent Hermes with a message to let Odysseus go. So Calypso did let him go and gave him wood to build a raft on which to sail home to his wife Penelope. Even though Calypso loved Odysseus, she sent him of in a good way not on a vengeful way.
"The goddess welcomed me lovingly, tended me, offered me immortality and eternal youth; yet she never won the heart within me. I remained with her for seven full years, and watered with continual weeping the celestial garments that she gave me. But when the eighth year came circling round, she told me and urged me to return, perhaps because Zeus had sent her warning, perhaps because her own mind had changed. So she sent me away on a firm raft, giving me many gifts, food and sweet wine, and clothing me in celestial garments; moreover she sent a fair wind for me, warm and kindly." - Homer, Odyssey 7.243