I mention non-human because one way to interpret Genesis (not correct, but being done) is that God took apes and upgraded them to get Adam and Eve. If that is true, then theoretically Cain might have married a non-upgraded ape.
You think Cain's wife came from Nod, and that is one possibility. Gill's commentary says you are wrong, and believes the Hebrew verbs imply Cain had his wife already. I do not agree with Gill, but it is clear that the case is not proven by your Scripture, as Gill consulted many authorities. Assuming you are right, and the wife is human and not from the garden community, then does that not prove that God created other humans who were not descended from anyone in the garden? That's a little hard to accept, since "Adam" is a plural noun. The word means "humanity" and was always interpreted that way, especially by the Jews, who ought to know their own language. Are you saying that God created many humans, and only favored some by putting them in the garden? The sin could only have occurred in the garden, since that is where the tree of the knowledge of good and evil was. If that is true, then the rest have not sinned, and so the Scripture that says in Adam ALL sinned is wrong.[/QUO"
Not only was Adam cursed but so was the ground he was made from. So any more people made from the ground were also cursed. Simples really. It just said that Adam was the first man made by God.....not to say he was the last.