I just finished reading again this webtoon and I think Sungyeon being overprotective with Hosik based on side story 2 page 2, where they are having a fight over having a body guard near at Hosik. You can see how Sungyeon is felt too anxious of leaving Hosik alone or just being far away with him even just a second. Look how the creator drew Sungyeon being so desperate.
Because as the past life of Sungyeon he left Hosik then came to him, seeing that he's dying. Maybe it's a regret or a promise to his past self? Or left behind feelings, that he must not leave Hosik alone. He just love Hosik so so so much. *now someone get me a tissue* (/TДT)/
I like the second couple more. I wish it should be longer. (/TДT)/