Return, O Lord, how long? rather, turn, O Lord; i.e. "turn from thy anger—how long will it be ere thou turnest?" And let it repent thee concerning thy servants. God "is not a man, that he should repent" (Numbers 23:19); and yet from time to time "it repents him concerning his servants" (Deuteronomy 32:36; Psalms 135:14).
He relents, that is, from his fierce anger, allows himself to be appeased, and has compassion upon those who have provoked him.