You and Hyunjin both have cystic fibrosis, a progressive genetic disorder that damages organs and makes patients vulnerable to infectionsy, but the both of you are dealing with lungs problem. Hyunjin is in the second phase out of three and you're in the first one, you still have hope to recover, but Hyunjins hope is slowly fading away. Since he has the worse phase that means you two can't touch or be too close to eachother so you wouldn't get even more infected by him