Even though the descriptions of these ethical views are somewhat simplified in the OP, I'd say I hold both Moral Nihilism as well as Moral Relativism too be somewhat accurate of my perspective on morality.
What is ethical isn't something that is universally agreed upon over every nation, culture, religion or even between individual humans. So, to me, that means it has to be something subjective; nobody is objectively right or wrong, since what is considered wrong is dependent on each individual persons environment during their upbringing and life. To believe that, simply because it's what You believe, it is the absolute truth is incredibly self-centered and small-minded imo.
But yea, I can also take a step back and objectively look at reality, which tells me that morality is not something that exist by some physical law in an environment outside our own (humans). It is a human invention, constructed for the sake of us wanting to make sense of the world, and neither less than often, forced upon us by the society we live up in.
"Moral nihilists consider morality to be constructed, a complex set of rules and recommendations that may give a psychological, social, or economical advantage to its adherents, but is otherwise without universal or even relative truth in any sense."
Wikipedia
That seems about right to me.