Dont give up bro, d2r is oldschool game, got tons of hidden master lvl knowledge which will help u tons, there are many strategies which will make duriel weak like a soyboy, example- u can get from npc that sells potions- antifreeze potion that gives u for 30sec +50% cold resi and increases ur max cold resi too, and u can give it to ur merc too, so basically u and ur merc will be invulnerable for any cold dmg duriel does, so only phys dmg will pose any danger.
Gearwise u gotta watch/read basic guides so u know what to look for, same build wise.
If u give more info and i know ur class/build i can give u more specifics or point u to where to look info how to gear/spec so its fun and ez smooth sailing.
Edit another thing about gear, ez to farm/buy is- runewords, if u kill countess in act1(its boss at lvl 5 tower) she drops very often runes, which u can use in runewords, very powerful stuff, and u can buy grey items with sockets for those runewords from npc blacksmith sellers, so not even any need to farm them