there is no "Chapter 139.5" in the manga series "Attack on Titan" (Shingeki no Kyojin) written by Hajime Isayama. The final chapter of the series was Chapter 139, which was released in April 2021.
In Chapter 139, there was no explicit information about Mikasa getting married or revealing her future spouse. However, please note that my information might be outdated, and there may have been additional content released . To get the most accurate and up-to-date information, I recommend checking the latest chapters or official sources of the manga.