That's one loaded question, Pessimist
Words can mean many things. Fiction and actuality are just that- words. Thinking with words gives us advantages and disadvantages; namely, worded thought can give us nothing more that approximation. As in science, statistics and mathematics, when the quantity of approximation grows within the data, the probability of an accurate conclusion or solution shrinks. (Of course, words vary in ambiguity, so judgements made on word count alone are not relevant.) This fact of language evokes a deep level of uncertainty. It is this fact of language, along with the subjectivity of interpretation that makes philosophy and art (especially literature) horrifying, yet beautiful.
With that said, I will try to differentiate fiction and actuality:
Fiction and actuality are both pieces of reality, and a differentiation and/or opposition of the two as worded concepts cause them to be defined by such a polarization. (In other words, the context the question "What is the difference between fiction and actuality?" redefines the words we are dealing with.) Reality is the universe (or multiverse, or what ever we want to call it). Within that reality is fiction and actuality.
Described in terms of action in regard to opposition:
Actuality: That which represents reality.
Fiction: That is not a representation of reality. However, being a part of reality itself, fiction can affect and cause effects that pertain to reality (like being affected by a touching film.) I'll mention this one last time: fiction does not oppose reality. In this context, fiction opposes actuality.
This definition has its roots the axiom that reality is defined as the physical universe- a definition that seems to infer that reality is objective. If it were rooted in the axiom that reality is subjective, then the answer becomes a lot messier. Also, I do not claim to be understanding and wise. I am uncertain. Although I sometimes enjoy convincing myself otherwise, I am not wise. Wisdom, to me, is a love and a dream- not a possession. It may be important to keep that in mind when reading/contemplating my post.