Since the question surrounds whether or not the advent of Jesus Christ is a condition of the plurality of the speaker in Gen 2:18, Jesus, when speaking after His resurrection to the two on the way to Emmaeus, made this enormously relevant statement in Luke 24:26:
Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken: Ought not Christ to have suffered these things, and to enter into his glory? And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning Himself. (KJV)
Here, Jesus was not one bit hesitant about going all the way back to the very beginning--Genesis 1:1--to "expound" unto these two Jewish men "the things concerning himself--Christ--Christos--the ANNOINTED ONE. Christos cannot be taken as a plural. So clearly there is room for a singular connotation somewhere in that portion of scripture.
Therefore, I will use the KJV to attempt to answer this great question about ch. 2 v.18.
And the LORD God said, It is not good that the man should be alone; I will make him an help meet for him.
Going back to the beginning, "Elohiym" (plural) created. We do not know what was said during that creation. No record is given here about God saying anything while He was creating the “heaven and the earth”. The only thing we can know for certain was that the result of that plural God's creation consisted of a single body of waters confined within a single area of deep space, each having a face--paniym.
In verse two, Jesus told the two men about the "singular" personalized "facet"--face--paniym--of that plural God--the Spirit--the ruwach--which reveals a certain "LIVE MOVING SPIRITUAL NATURE" of God. In verse 3, FINALLY we learn about another very important aspect of Elohiym. HE SPEAKS. So we can be certain that Jesus told the two men about the facet--face--paniym--person of God which is "His WORD." In verse 4, Jesus, no doubt, also spoke to the two men about the plural Elohiym being a seeing God--and God SAW.
Genesis chapter one deals with the plural God repeatedly setting out certain project plans. Then, the Word of God--a certain facet--paniym--person of God is shown as carrying out those plural Elohiym's plans. Thirdly, the Seeing God--a certain facet--paniym--person of God inspects and approves those inspections. Moreover, the sovereign plural God "defined" when God called something by name, and "commanded" certain things as God's law. We see this happen over and over again throughout chapter one. These faces--paniym--of God are highlighted in each instance--each in that facet's own lane, yet together as one plural faceted God. Throughout scripture, God's various and voulmnous names always each seem to describe a single facet (face) of the one Lord God.
John 1 1-3 declares:
In the beginning was the Word, and the Word was with God, and the Word was God. The same was in the beginning with God. All things were made by him; and without him was not any thing made that was made.
In chapter two, verses 2 and three, the plural Elohiym ended His work. Certainly, Jesus told the two men about the combined work and the combined rest of all of those facets of the One True God, combined.
Yet, as we know, Deuteronomy 6:4 insists:
Hear, O Israel: The LORD our God is one LORD:
And the same Jesus who expounded unto the two men about the plurality of the LORD God certainly explained His UNITY with the ONE but many faceted LORD God who just happened to be SPEAKING in Gen. 2:18 as well as in in John 10:30:
I and my Father are one.
I believe that this instance in Gen. 2:18: is describing the LORD God in the singular sense (I will) of ONE who is the many faceted, but ONE LORD.