Theophylact of Ohrid

Only a certain young man followed Him. This young man was probably from the house in which they ate the Passover. Some, however, think that this was James, the brother of God, called the righteous, for throughout his whole life he wore a single cloak, and after the Ascension of the Lord he received from the apostles the episcopal throne in Jerusalem. It was he, they say, who left behind his outer garment and fled. And there is nothing surprising that, when the chief apostles fled, he too forsook the Lord.

Commentary on Mark ↗

Gregory the Dialogist

Or, he says this of John, who, although he afterwards returned to the cross to hear the words of the Redeemer, at first was frightened and fled.

Catena Aurea by Aquinas ↗

Bede

For that he was a young man at that time, is evident from his long sojourn in the flesh. Perhaps he escaped from the hands of those who held him for the time, and afterwards got back his garment and returned, mingling under cover of the darkness with those who were leading Jesus, as though he was one of them, until he arrived at the door of the High Priest, to whom he was known, as he himself testifies in the Gospel. …

Catena Aurea by Aquinas ↗