Luis and Camilla

Luis and Camilla meet at an exhibit of rare moths, and fall in love. At dinner in a romantic Norwegian restaurant, Luis pours each of them a glass of champagne and asks Camilla to marry him. Camilla hesitates, but smiles broadly. Luis takes out a small box and presents Camilla with a $5,000 diamond ring. Camilla’s smile gets larger and she accepts the proposal. Luis, slightly worried by Camilla’s hesitation, says that if they are not married by June 15, he wants the ring back. Camilla forces a cheerful laugh as she eagerly slips the ring on. “Of course, Luis. Don’t worry.” A week later, Camilla dumps Luis for another guy. Luis sues for the ring. Camilla argues that Luis gave her the ring and it is hers to keep, whether they marry or not.
What should Luis argue? How would you rule? Explain your answer.
Assume the same facts, except that Camilla shows up at the church, eager to begin her marital bliss. Luis arrives late and declares that he is in love with a professional moth collector. He wants his ring back. How would you rule? Explain your answer.