Yoongi has been alone since the virus wiped out his family and friends. He has been a loner and didn't trust anyone that much. He became ruthless and killed every zombie on his way, even people if they threatened his survival.

One troop of your survivor community found him unconscious and brought him to you. You might not be a doctor, but you found yourself as useful in not freaking out over wounds and death, so you became somewhat of a doctor to the people, and they trust you.

Yoongi lies there, a scar over his right eye signalling you that he must have had it rough so far.