Nozomarenu Hanayome wa Ichizu ni Koutaishi wo Aisu

When her country of Lidea loses the war, Princess Tinalia must wed the enemy prince, Keith. The arrangement isn't as dire as it sounds, though: after all, Tinalia has been in love with Keith for years!

Unfortunately for her, Keith doesn't remember they already know each other. The circumstances of their first meeting were unfortunate, as their countries were at war, and Lidea committed too many atrocities against his people to forgive. Thus, Tinalia finds herself the hated bride of the crown prince, treated coldly and scornfully by everyone around her... even though she continues to love him with all her heart.

(Source: Tokyopop)