Stark was previously hailed as a hero because he saved the world from a deadly being quite recently. Later he expected that life would go well for him but it turned out the exact opposite way. His personal life has no chance of betterment and his professional life has just turned into ashes. The only thing which used to make Stark happy was the peaceful situation of the world.
The peace of the world also starts deteriorating when a virus starts eating up everything. King Bullet is behind everything and he wants only one thing in life i.e massive destruction and bloodshed. Dealing with such a mad being is not easy and Stark has all the time in the world to tackle the situation.