I, too, had quite a time with this little pipsqueak!!
But, I learned to NOT use an enchanted weapon against him AND to stand near the temple door so I could take a quick exit to rejuvenate.
ALSO, I would cast all my Summons spells before entering the fray again. That at least kept him busy while I whacked away with my non-enchanted longsword. OHHH...and you should boost your own LUCK as much as possible between each series.
I finally did kill him and then carried the ebony armor to the smith and sold it.
(Well, as much as I could sell before he ran out of money.
)