Is there some other word like nostalgia that explain how one who has to leave their home for external circumstances, and misses everything but can't go back?
The Galician word morriña defines perfectly the melancholy or the sorrow that Galicians feel when they are away from their homeland. Morriña is a very deep, nostalgic and melancholic homesickness experienced as one intensely longs to return home. It is often described as “a ‘saudade’ so strong it can even kill”.
Saudade is a Galician and Portuguese word for a feeling of longing for something that one is fond of which is gone. It often carries a fatalist tone that the object of longing might really never return. The word morriña is synonymous. Both words are intimately linked with the huge numbers of Galicians (gallegos) who were driven by poverty and opportunity to migrate from Galicia, first to the Americas and later to the rest of Spain. ― Iberia Nature, ’saudade – morriña’
The Real Academia Española describes morriña as tristeza o melancolía, especialmente la nostalgia de la tierra natal (sadness or melancholy, especially the nostalgia for the land of one’s birth).
