Adam Clarke on John 13:23

Now there was leaning on Jesus' bosom - The Jews of those days, at their suppers, reclined, supported by their left arm, on couches placed round the table, as the Greeks and Romans did. On each couch there were two or three persons; and the head of one of them came near to the bosom of him who reclined above him on the same couch. The person here mentioned was John, the writer of this history, who, being more tenderly loved by Christ than the rest, had always that place at table which was nearest to his Lord.