"My dear sweet child..." The Queen put her arm around the dejected teen. "You can't win what's not offered."
"But I love her!" he whined.
"Oh how I know! Believe me, I've been in the same position." She squeezed him tight against her bosom. "Most of us have. Loving someone who loves someone else..."
"What did you do?" He was suddenly very unsure where his hands should go, and desperately trying not to look at the cleavage mere inches from his eyes. To his horror and thrill he was pulled in even tighter.
"I? I went out and got what I wanted. I didn't let anyone or anything get in my way." Pulling him from her chest, she cupped his face in her hands, and pulled him toward her face. When they were nearly nose to nose, his eyes as wide as saucers, she said "If you want her heart... you have to take her heart. Show her you're a man. Are you up to it? Do you want her?"
He nodded, and she kissed him full on the lips.
"Good. Then let's see that you've got the tools for the job."
The following day he was back, with his beloved on his arm. "It worked." He grinned like a fool, and held up the box. The sanguine glow leaking from the edge was faint but steady.
The Queen stepped from her throne. "Congratulations, and well done." She took the box gently from the boy, and cracked the lid. "Excellent indeed..." She pulled the knife from her hip sheath and handed it to the girl. "Now cut his heart out."
As she did, the Queen added the box to the growing collection on the shelves behind the throne.
These magic boxes allow the owner to draw the heart from a single individual. That person can make a save vs spells. Failure means their heart has been magically removed. They will say or do anything that the holder of the box orders, an effect more powerful than any standard charm spell.