Me and my friend have been playing the game from the classic version on Game Ranger due to b.net not working the way we exactly want to (port forwarding and such) and from Butcher to King Leoric/Skeleton king, it took us almost 50 mins to town portal+heal kill attempt King Leoric/Skeleton King but for some weird reason he doesn't die. I'm a Rogue with armor lowering atribute while my friend is a Warrior tanking Leoric/Skeleton King but we feel like no damage is being done or if the game is just absurdly hard. We aren't attacking with any magic stuff and I know he's strong against it so i'm just suprised...

If it's a patch upgrade from the vanilla 1.0 diablo, then it feels like they made the game like dark souls lol!

Anyone else have any problems like this?

In multiplayer, The Skeleton King has the unique ability of 100% life steal. Every single point of damage he does to a player character is added to his own hit points, even exceeding his normal maximum. This is in addition to the regular healing that all monsters get. Regular healing stops when current hit points are greater or equal than maximum hit points. If you're retreating to heal, that suggests you're taking substantial damage in the fight. This is fine if the damage is from the minions. If it is dealt by the Skeleton King directly, then he will benefit from it. You want a combat plan that, even if it deals damage only slowly, minimizes the life stolen from you.

How is your warrior equipped? How much damage have your characters taken? How often does your warrior block attacks from the Skeleton King?

Buy a scroll of Fire Wall at Adria and have Leo stand in the fire while your warrior keeps him in there. Should help ya.

It is not uncommon for players to skip Butcher and Leoric and come back later at a higher level.

This might sound counter intuitive, but you may have a better chance if the rogue tanks.
If you distributed stat points like most people (which isn't quite optimal), the rogue would have a higher Dex rating. The higher dex not only let her land more hits on Leoric, but it will allow her to block much more efficiently to lessen Leoric's Life Steal.

Remember blunt weapon and shield.

Holy Bolt works wonders. Low level Holy Bolt spells also do tremendous damage.

Holy Bolt deals damage in the range [9+clvl, 18+clvl] (according to Jarulf's Guide section 4.1.3, page 69). The Skeleton King is mlvl 14 in Normal difficulty (5.2.2, page 92). To stun a monster with a spell, you must deal damage >= mlvl+3 (6.3.1, page 143). From this, we see that you need to deal at least 17 damage to stun him. Any character level might deal this if you roll a max damage hit. To guarantee that every hit stuns, you need to be at least clvl 8. Regardless of your guaranteed damage, you also need to reliably hit him. According to 6.3.1, page 143 (yes, again), FTHspell = 50 + Mag + bonusplayer - 2·mlvl. That will likely make it difficult for low level non-sorcerers to be effective here.