I think you mean this one
https://www.mangago.me/read-manga/highschool_boys_trapped_in_a_fantasy_world/
It has:High school boys, going to a different world in a dream, MC encountering a slime early on (though it didn’t melt his clothes xD), warrior ML
If I remember it correctly it’s on webtoon, so it’s better to read it there to support the ......
