A promise made when you were a teenager is just childish words, but if the other person is very important to you, how long will you remember it?
"I don't know if you remember that agreement, so I'm very scared, afraid that you will forget it, or that you will just mention it casually. I have met people with the same name as you, but they are not you. I don't know when I will meet you, and I am afraid that I will never see you."
"You are so stupid. I promised you I would come to you and you will definitely come. I just made you wait for so many years. I'm sorry."
It doesn't matter, I will meet you later and I will be you for the rest of my life.