- czemuś mnie opuścił = why have you left me, why hast thou forsaken me (archaic)
English Translation
My God, my God, why hast thou forsaken me?
czemu + ś (from opuściłeś)
It’s important to note that this is rather archaic, elevated literary language (it’s because this particular quote is from the Bible). Nowadays one would say “dlaczego mnie opuściłeś?”.