IMO:
Mark D committed suicide.
To me it seems those who do that are sometimes so hurting, they are selfish.
A note to say whatever their final words might be would be so helpful to family, even if it is hurtful.
Instead, they found a goodbye note. The note expressed his love toward his parents and family, and claimed it was nobody's fault that he left, but that it was just something he had to do.
"Mark stopped going to most of his classes after Thanksgiving," Randy Davis said. "Later we found out he only completed one of his courses, a Spanish class in which he earned an A. There was no confrontation between us, and since he had so many hours we just told him to take a year off and figure things out."