Caramel Glow

In Mello's case, I think he would have had a much happier life; the presence of his family, a more genuine and healthy social life, no children overshadowing him. Perhaps he would have had obsessions, but never ones as toxic as the one he had with L.

In Near's case, I think it would have been the complete opposite; a emptier, lonelier life. He wouldn't have had any challenges, he wouldn't have received as much attention as at Wammys, and some children might have treated him badly for being different.

Maybe he was one of those unpopular kids who were bullied and suddenly became popular and a bully after finishing school. Maybe that's why he persecuted Thanos so much and tolerated all his disrespect (he saw it as a way to be popular, maybe as a shield; no one would mess with him), and for that same reason, he felt so angry when people looked down on him or saw him as a fool. He hated Thanos for not giving him the place he wanted, he hated Se-Mi because she made him feel inferior, he mistreated Min-Su because it made him feel more powerful. Maybe he even hated Se-Mi and Min-Su because Thanos "defended" them.

I dare say he even tried drugs for the first time when he was working at the club because he thought it was cool, but he was very mentally weak and ended up becoming addicted.