Nathan took his sword and marched towards Aeinshia. His steps fast and low in there movements. This is it. This is his last chance, either he will be killed in hands of Peter or use Aeinshia as the bait to escape. Being a black pawn, it is no shameful thing or any wonder if he chose the latter option, however, being a man, his pride definitely felt a lash in it, to use a woman as his shield to get away alive from here, instead of facing the knight who came to fight with them.
The single man managed to kill already more than half of his brothers present in the cave, which only implied that Nathan isn't really a competition to Peter. They didn't have a one to one fight and fought in groups with Peter, even then,the victory followed Peter, which shows his superior combat skills and swordmanship,and if Nathan denied it, then he is only a fool, who got no idea about himself and his strengths.