Complex sentence: They would have been young again, for several more centuries, but in the sorceress's opinion, Tristran would only break the star's heart, waste it or lose it, as the witch-queen believes that is what all men do eventually.
Split into simpler sentences: They would have been young again, for several more centuries. In the sorceress's opinion, Tristran would only break the star's heart, waste it or lose it, as the witch-queen believes that is what all men do eventually.