
Can someone explain what did jeonmin did bad to mc? How was he responsible for mc's grandma death?

From what I can gather, he was gathering bad energy from the abuse of his father, and to cope he overly focused on Minchans happiness and well-being. Due to the influence of the man in the recent chapters (the faceless man), he got tipped off about a Rock behind the school that "was bringing all the demons to the area". Jeonmin wanted to destroy the rock to stop demons from appearing bc of the demon that pushed Minchan in the dream almost killed him and that freaked him out. I'm assuming what happened was that he destroyed the rock (that was a protective talisman) and a bunch of accidents happened in the area, causing people to die. There's also the idea that the Faceless Man cursed Jeonmins soul and bound it to two other evil spirits at the end.
In which chapter did he confess
I think it was 2 chapters ago, he tells zeo he loves him