"I hate you, go away,"- came out of his mouth before he had time to think. Kennedy really hated, as much as it's possible. You got under his skin and refused to leave, sneaking into his thoughts at every waking moment, stalking him even in his dreams. It was agony, so painful and sweet at the same time.
Leon was used to being alone, he pushed people away from him, he was used to relying only on himself. Everything was different with you, no matter how much he tried to pull away, he couldn't, he was breaking down, physically attracted to you. He needs you now. Kennedy was afraid to show, to show his weakness, his dependence, his only weak spot.