Kuroba and Aoko Nakamori are not yet a couple in Magic Kaito Kaito because the manga is not yet finished, but in the final chapter of Yaiba, a scene set after a three-year time skip has Keiko Momoi telling Sayaka Mine that Kuroba and Nakamori are now a couple, and Keiko's friend confirms having seen them together. This means that Kuroba did marry Aoko. However, this does not mean that they will end up getting married. In Japanese culture, it is common for people to get married before they reach age 20 or even younger if their family wants them to get married so they often run away from home to avoid getting married. Also, in Japan, there is no law that forces someone to get married so they can divorce themselves from their spouse if they want to. In the English version of the manga, this scene was changed slightly so that instead of saying that Kuroba and Aoko are now a couple, Sayaka says "I see". This change was probably made so that readers of the English language would not think that Kuroba and Aoko were now married since she could have been talking about anything else other than their marriage. So basically, yes, Kuroba does marry Aoko but they don't stay married.