I'm so close to quitting the game

I have been stuck at Erlang for 12 Hours (2 Days) and it's getting really frustrating by the day.

Closest I've gotten him down to was 1 HP, literally, and never again. I've tried the various cheeses and everything but it's still not working out for me. Do I even bother? I got work starting next week and I'm borrowing this game from a friend💀

(Using Pillar stance and lvl 86)

EDIT: THANK YOU SO MUCH EVERYONE FOR THE TIPS😭🤝 I've decided to farm and grind abit just to ensure I'm leveled enough (currently lvl 116) & planning to change my armor set, any reco? Also, any tips to increase my damage? ( I have maxed crit chance & dmg along with using the Bishui staff)

EDIT: I did it, finally beat him with those useful tips below, and on my 4th playthrough ✋🙂‍↕️