One opposite of love, like hate, though neither mutually defines love.
What causes fear?
I fear a threat or a danger, something that might harm me. The darkness sometimes scares me for it may hold something sinister.
I evaluate these possible threats, these dangers, relative to how I identify myself.
If I am my body, then things that may injure me or cause me disease are fearful.
If I am my mind, thoughts that might threaten my sanity or my ability to perceive my environment are to be feared.
If I am awareness, I fear what steals my attention away from the Truth, the self-deceptions or delusions that lead me to set intentions that isolate and separate me from what-is.