Synonyms for Endlessly (same or very similar meaning)
WordNet sense 1 ((spatial sense) seeming to have no bounds):
without endWordNet sense 2 (all the time; seemingly without stopping):
interminablyWordNet sense 3 (with unflagging resolve):
ceaselessly, continuously, incessantly, unceasingly, unendinglyWordNet sense 4 (continuing forever without end):
infinitelyFrom the ODE community, based on WordNetadd/edit