Hoshi no Koe

To what distance would you go for your one true love? In a future filled with a boundless potential for interstellar peace and prosperity, Mikako joins a research team to explore the recent contact between humans and alien races. She ventures out into space, leaving behind Noboru, the one young man she loves. As she travels deeper into this new frontier, her only connection with her boyfriend is through cell-phone text messages. But the years pass, and Mikako barely ages in the timelessness of space–while Noboru grows older and considers moving on with his life…In this timeless romance between star-crossed lovers in the most tragic of settings, there are some places man may not be ready to go. Summary taken from Manga-Sketchbook.