
Why and how does he still love him

Will the uke was gangster to begin with so he was already involved with drugs, so him ending up as addict is his karma, it not like he was normal law binding citizen who got dragged into this life, he was already part of it, I don't support him getting tortured but I think he did same to others, not to the extreme that he went through but he not all clean himself.

If you try to seek justification, this manhwa actually none at all provide it. Uke might find his karma, but what about seme? Where is his punishment? Who is he having a master hand of everyone's life?
Until the end he face no consequence at all.
Blaming uke for his past for his now treatment is not fair, because the monster of all this can live as he wants.
I like sir Melmont's reactions