I would like to ask if the romantic kind of love is an emotional thing or a duty.  Thank you.

It is not an either on or the other, it is both a duty and emotional.

Romantic love is something married couples are bound by duty to give to each other. "Let the husband render to his wife the affection due her, and likewise also the wife to her husband" (I Corinthians 7:3). But at the same time it can be a duty filled with emotions. When the young woman in the Song of Solomon realized that the king was truly in love with her, she said, "Sustain me with cakes of raisins, refresh me with apples, for I am lovesick" (Song of Solomon 2:5). In her later years, she described love very passionately: "Set me as a seal upon your heart, as a seal upon your arm; for love is as strong as death, jealousy as cruel as the grave; its flames are flames of fire, a most vehement flame. Many waters cannot quench love, nor can the floods drown it. If a man would give for love all the wealth of his house, it would be utterly despised" (Song of Solomon 8:6-7).

See also:

Questions and Answers regarding Marriage
Questions and Answers regarding Love