Question: why rhaegar fell in love with lyanna?
Answer: Rhaegar lied. ... Lyanna was the “Knight of the Laughing Tree,” a secret Rhaegar learned and kept for her safety, and he fell in love with her for it, and she fell in love with him. It's why she stole away with Rhaegar a short time later, and why he had the Kingsguard protect her during Robert's Rebellion.