Why not use metaphor as Emily Dickinson has done in her poem about hope whose first stanza reads,
“Hope” is the thing with feathers -That perches in the soul -And sings the tune without the words -And never stops - at all ....
Looming over the heart,
That will not rain forth aloud,
Or muster wind enough to depart,
But shadows the soul with its lifeless gloom throughout.
OR--Here is an example of a simple metaphor (life=gloom) used in a declarative sentence:
Hopelessness can loom so darkly over the heart that one's life is none but gloom.
There are many different ways to say the same thing. Some ways are more creative than others. So, I will give you several different versions.
A simple inversion of the sentence is a follows: "An unhappy life is often caused by hopelessness."
Another version is as follows: The one who has no hope in life may be unhappy."
A more pithy was of saying this is: "unhappiness is rooted in hopelessness."
Here is a more figurative way to say it: "Hope leads to happiness, but hopelessness leads to unhappiness."
These version should get you started.