He was slightly jealous of the owner of pun-chan when they were both in the same highschool because the owner had everything the neighbour wanted in personality,position and friendships in those days. So he doesn't want pun-chan to belong to him because he thinks the owner still has everything going for him in life, same as it was in highschool. (He doesn't hate him though). So him being pun-chan's owner would be him having another thing is likes/wants.