The way things are going, it's probably someone else and not Alan who did the cursing.
The person probably used Alan's ring so it would seem that it was him if the curse was discovered.
Alan is obviously also being affected by some sickness or curse.
Someone tried to kill Dario too in the previous chapter, and it wasn't Alan cause he simply disappeared like an illusion, though it wouldn't explain the big whole created. With the title "hero", I don't think Alan would have the skill to do something like that, let alone if who we saw was the real, sickly Alan.
My bet is on the sage too. If it actually was the healer I would be surprised since even if they turn out to be evil, they don't normally work alone, if compared to other mangas.