Dexterity (DEX)
 

why does dex increase Endurance ? shouldn't it be attack increase ?

as far as I remember only stam should increase Endurance or

All melee stats contribute to your endurance total at least as far back as the LDoN client, dunno about earlier. It's clientside, in any case.

Affects: Concentration (resistance to spell interrupts), Bard Song missed notes; Melee skill-ups, Procs, Crits (allegedly).

Max (cap): 255 (?)

Brad McQuaid: "DEX: how quickly you learn weapon skills; how often weapon will proc; how quickly you learn rogue skills; how hard you hit with bows"[4]

"This determines how hard you hit with your bows, how quickly you learn weapon and rogue skills, and how often a magic weapon will process it's skill. This is a good skill to have for fighters, especially rangers and rogues, and of only limited use for magic users."

so nothing about endurance just stats to improve melee damage

This server uses unclassic endurance (instead of stamina). This iteration of endurance does take Dexterity into account.