Aries:people leaving/the thought of people leaving.
Taurus:they don't have everything they want and they don't know what they want.
Gemini:themselves, feeling distant from everything and not knowing who they are.
Cancer:everything. Nothing. No one knows, they don't either they're just sad.
Leo:not being trusted or being looked at as irresponsible and untrustworthy. Also being betrayed when you trusted someone.
Virgo:life not being how you pictured it, not being able control a situation.
Libra:overthinking, being under pressure/being overwhelmed, stress in general makes them sad.
Scorpio:themselves, their life, the situation they're in and the life they were born into.
Sagittarius:sad situations around them, sad events. An empty kind of sad, not getting their way.
Capricorn:feeling hopeless, not knowing what's next, not knowing the future, and being spontaneous.
Aquarius:themselves and how people treat them, how they see the world.
Pisces:other people's opinions of them. Other people not liking them and giving someone you really like a bad impression.