Yep, mariek is correct. There is no reason to have an accusative, so your first choice is correct.<br /><br />As for word choice, yours are valid, but I might consider
perpetuae instead of
aeternae. This is because
aeternae has a sense more along the lines of "eternal" or "throughout the ages" while
perpetuae means "ongoing", "everlasting". They both do mean forever, but each has its own nuances, and few words are going to fit with your English perfectly (which is why it is so much better to learn a language than read translations

).
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae