A single word for "the space in between"

Interstice:

a space that intervenes between things; especially : one between closely spaced things. Eg, interstices of a wall

I suggest gap. It needs to be paired with between.

The gap between fear and love is filled with uncertainty.

However, space, as used in your question, is at least as good.

They're somewhat poetic but "rift" or "void" have a visual quality to them that may help illustrate the point.

Lacuna is my favorite.

a blank space or a missing part

Abyss, hollow, cavity, valley, interval, lacuna, gulf, silence, caesura, division, ravine, vacuum ... it all depends on what image you wish to convey, really.