I remember reading a webtoon, there's this girl who took care of a slime from some cave or something with talismans or letter thingy hanging, the slime can change form into man, and the girl has a crush on his superior(?)and one time this slime changed into his form and fcked her, I remember the slime going into the girl's work and changed form into woman? or just a beautiful man?Yes its hentai, i remember also the slime fucking multiple people, woman and man with his tentacles and the people saying he's so good and begging him. even tho i didn't wnat to ask this since it will chop of half of my whole life's worth of pride, unfortunately its really bugging me...please help

My Special Squishy Someone. No clue if this is it or not, but it does sound like it might be... Also, it was the only result when I searched for slime in manhwa...

Edit: Now that I've read it I can say with some certainty that this is the one you are looking for.

~4400 manga completed
~1700 ongoing...