Hoshi No Koe

From Tokyopop:
To what distance would you go for your one true love? In the midst of an alien invasion, Mikako joins the resistance, leaving behind the one young man she loves. As she goes deeper into space, Mikako’s only connection with her boyfriend is through cell-phone text messages. The war rages on and years pass, but Mikako barely ages in the timelessness of space while Noboru grows old. How can the love of two people, torn apart by war, survive?