Maybe he fell in love the first time they met, and he didn't know there was someone living in his heart. That person was by his side and showed great affection to him, but that person happened to be an internal agent of the enemy country. Binghe was helpless towards Shun.
Maybe he shouldn't have been tempted in the first place, but he knew that he had lost the chance to regret it. That person trusted him and cared about him, but he was standing on the opposite side of that person. Shun is always on the glacier.
Binghe: Regardless of my status, I only know that you are the one I care about most.
Shun: No matter where I am or where I am, I only know that you are my home.
Regardless of the vicissitudes of life, I am willing to go with you.
Purpose: To give a good story to your favorite character. That's all.