My theory about the 2 couple : Isaiah and Gabriel have the same eyes (one functional and the other not). I think Gabriel was created using Adam and Eve's DNA. Then they took Gabriel's eyes and gave them to Adam like he lost his sight as a side effect of the guidance with Eve . And since it was too cruel for Isaiah to get rid of Adam's clone, he gave him one of his own eyes and kept him by his side while Adam took care of Eve.  And then Eve erased his and Adam memories like this they can live each in their side and forgetting the other