He had the walls between the two rooms knocked down and rebuilt, thinner, so that if any sort of struggle took place in Nokoru's room, he'd be sure to hear it. Of course, this arrangement wasn't perfect. There was always the fear that someone could carry Nokoru off without a struggle. Drug him, knock him out before he could yell, or any other number of insidious plots that probably occurred more readily to Suoh than to any potential kidnappers.
Or murderers- but that was something Suoh never wanted to think about.
Then, the world was falling in on them as one of the final earthquakes trembled across Tokyo. It had caught them off campus and off guard, and Suoh shielded Nokoru with his own body. After Suoh was released from the hospital, something seemed to break open for Nokoru, and before Suoh knew what was happening, a sobbing Nokoru was in his arms, kissing all over his face in relief.
Now Nokoru sleeps with Suoh's arms tight around him, and Suoh knows that Nokoru is safe.