Responses
He couldn't take it anymore,, drugging the concubine and making the emperor, (who killed his son mercilessly) happy
It was out of spite and for the sake of revenge. He was the only doctor who could concoct the medicine that "cured" MC's depression. So when the doctor committed suicide, he actually took the ml's hope of mc getting better and accepting him as well as making mc more miserable by taking away the only medicine/treatment that was keeping him comparatively sane.
Why did the doctor kill himself??