--I understand they may seem a little trite and/or overused, but when utilized correctly, fireworks make the scene that much more dazzling. +10 points if it ends up being a tragic death scene, and the significant other's last words are: "Look how pretty they are..."
Similar objects: fireflies, stars, secret waterfalls under the moonlight.
--Whether they end up being the solo instrument in the background music or even being played by a lover character, pianos are that wonderfully versatile instrument that can amplify almost any emotion.
--Especially if the couple marvels the falling snow from a particularly high place.
--I am ABSOLUTELY ARDENTLY INFATUATED AND OBSESSED WITH scenes in operas/musicals in which the two lover characters sing a duet together. They're just so beautiful.
Bonus points if the duet is in a foreign language.
Extra bonus points if it's a Romance language (Spanish, Italian, French, etc.).
--Whether it be the more common worried housewife/girlfriend feverishly concerned about her husband/boyfriend on the battlefield or the slightly less common situation in which both fight together, war really emphasizes on a specific trial (out of many) that can challenge many relationships. It goes to show that the strongest of love can endure many things, even in the face of injury, suffering, and death.