The meaning of this sentence was: When there's someone in my heart, she's in my heart. Even if she's not in my world, there's still a place in my heart for her. However, the deeper meaning of this sentence was: A person's feelings were complicated and not a simple addition. Even if her heart was filled with someone, it did not mean that she would always be there. Not having her in his heart did not mean that she did not exist. This sentence expressed a deep and rational emotion. It meant that he knew that feelings were dynamic and not static. He did not want to put pressure on the other party and did not want to leave regrets for himself.