BE (Bad Ending / Tragic Ending) typically means the main character dies, the central relationship collapses, or the protagonist's goal fails. BE does not equal a bad book — many literary classics owe their power to tragic endings (e.g. The Song of Achilles, No Longer Human).
The emotional cost is high, especially if you are sensitive to themes like suicide, character death, or war. Use the trigger warning matrix to decide whether to read now, postpone, or skip.
If you want a lighter form of melancholy, see the Bittersweet Ending list instead.