Well my advice is : DON`T! You dont have to to go on so leave him. IF you insists well his main attack is firebased (?) so raising fireresistans with elixir or protection with spellsheild should help. I assume you have a bunch of minor restoration potions? If not get Alchemy and mix some ASAP. As long as you heal the damage faster then he puts it on you have a chance.
