Read carefully the passage: near the cross of Jesus John (the best disciple) is not mentioned among the women found there.
Where is then John in this scene?
He is not under the cross. He is on the cross. The his body is possessed by the Spirit Jesus. This is the reason the spiritual Jesus "saw" the mother and the Beloved Disciple "standing nearbly": he has just abandoned the body of John (on the cross), and he therefore is going to see from above (from heaven) the mother of the Beloved Disciple (under the cross) and the Beloved Disciple (on the cross).
Then, by saying “Woman, here is your son,”, the spiritual Jesus is saying that the mother of the crucified victim will have again the body of the her son, after that that same body is abandoned now by the spiritual Jesus.
By saying, “Here is your mother.”, Jesus is saying to the crucified (=the Beloved Disciple) that he will become again mere property of the mother of him (=John): a carnal mother. The demiurgical mother, matter.
THe mother is the same NEGATIVE figure of the presumed "mother" of Jesus in Mark.
Therefore she is not the real mother of Jesus. This is the reason she is rejected by Jesus in Cana ("what between me and you, woman?").