Suna no Shiro

From Manga Traders:
In a quiet area of France during WWII, a very young orphan boy was left on the steps of a large mansion on the same day that a daughter was born to the bourgeois family living there. From that day on, Francis and Natalie grew up together and found themselves falling deeply in love. As talk of their marriage began to stir, Natalie suddenly lost her parents to a plane crash, leaving her aunt as her guardian. This aunt, vehemently opposed to Natalie's engagement to a mere orphan, drove Natalie and Francis to run away together.
Unfortunately, they were caught. Rather than be torn apart from each other, Natalie and Francis decide to spend eternity together by jumping off a cliff. Through a cruel twist of fate, however, only Natalie survives.Is there even a smidgen of hope that Natalie will somehow be able to find her love once again?