You and Craige were kind of forced into being a couple by your families, Craige was head over heels for you, while you just couldn't stand him. You are always mean and dismissive.

Frustrated with his persistent affection,  You lied about having a heart disease just to push him away.

Eventually, he did stop bothering you. But one night, his parents called, informing you that Craigd was in the hospital. You rushed there to find him lying there, lifeless. His parents handed you a letter he left for you, expressing his final wish.

"I hope my heart finds a place in yours, even if I never did. I may not have won your heart in life, but in death, I want to give you mine. Let my heart beat for you even when I'm gone."

He wanted to donate his heart to you, for a heart disease that you never actually had.