On the day of Blue's eighteenth birthday, he attempted s*icide. The previous day was the second day of his heat cycle.
On the first day of that particular heat cycle, he had refused his father's orders—which was to spend his cycle in the Heat Room.
After Preston Kent, Blue's father, realized that a Dominant Omega could lose their Dominance without proper care from an Alpha, he designed the Heat Room in the basement of the Kent House.
The room's purpose was specified in its name. It was a room wherein Blue would pass through his heat. As for Eliot and Atlas, they were both Alphas. They could go out into the world and spend their rut with any lucky Omega they found attractive.
As for Blue, he was thought to be a weak Omega, who would dare send him out during his heat?
And so, Preston arranged for Blue to receive temporary marks from different Alphas he thought were worthy during every single heat cycle of Blue's.