Romantic does not mean the same thing for every couple
Some couples want peace and privacy. Some want restaurants and nightlife. Some want adventure and scenery. Some want an adults-only all-inclusive where the whole point is to think less. Some want beautiful beaches and easy logistics because hard trips do not feel romantic to them at all.
The wrong destination can look romantic online and still feel boring, too quiet, too expensive, too busy, or not practical once you arrive. The better question is not which island is the most romantic. It is which island fits how the two of you actually like to spend a day.