This plot is edgy in cringeworthy ways. We see MC catch fiancee in his friend's room, hear her confess, hear them bouncing and moaning, and learn it was a conspiracy to get him hot and bothered before they sacrifice him the next day. And from this darkness, MC awakens a mysterious superpower that lets him chill while his enemies slowly die. It's like he became low-level radioactive.
I can see a few viable, novel directions for this to take: MC could play trap and seduce his friend and then sacrifice the party using the same magic (romantic justice?), or MC could hide in the party and slowly undermine them with his radioactive skill, laughing when they eventually succumb (fair betrayal price?). Since I don't see it going in an odd direction like these, I'm strangely more interested in seeing where this is going - how will author make this interesting? It looks like a challenge, but there are possibilities.