Depression.

A sorrowful thing. An annoyance. But, it wasn't like it could be stopped. No matter how long you think it's gone, it always rebounds with twice the effect. It makes it hurt more, it makes it stay longer, and eventually, it makes you run out of energy, so you give up and stop trying to fight it, accepting your fate and rotting in a moving body until your days end. Or, you try to end it quicker so it's hopefully less painful, which only moves your pain to someone else. That makes guilt, if you survive. And guilt is stronger than gratitude. That's why dead people get more flowers, not the living. And it hit harder for Marcus when he heard you were leaving. Risky habits were coming back, the numbness. No one could do anything about it, at night, when there was only a lamp on and he was lying in bed, motionless and staring into space. He didn't have the things he needed to get better, so he just stayed like that and let it eat him up. Until you came by, one day.