If he did take the drugs... it isn't just because he got it from being in a relationship who uses drugs as a sort of escape from reality. It's also becuase of the stress and pressure of hiding. If one is comfortable of themselves and open about who they are and who they're with, they won't be tempted to try any bad habits.
It's like... a guarantee that their relationship is gonna end soon, (depending on what kinda drugs you take I guess) and someones probably gonna die, especially since they don't seem too close with their families.. I like to think that these couples are happily together for the rest of their lives. It's like harada added that extra because they think such a happy ending isn't fit for such a dark and twisted story, or a relationship that started out badly.
Harada's stories are rarely far from reality... So him adding that last part is just a continuation of what it is like to be in that kind of relationship.
It ain't like disney where everything ends with a happy ending, coz in reality, being in a closeted relationship in a society where relationships and orientations like that aren't accepted, you either become a fighter or use stuff in order to escape reality or both, a fighter who uses stuff...
It's harsh but real. That's what Harada's stories are like. (Which is why I avoid em when I'm feeling happy, even though I've read every single one. xD)
Harada's stories actually make me happy, they seem to have just the right amount of twisted stuff, unexpected stuff, and yet also have enough goodness to balance it out and make it seem ok? It's comforting, like no matter how messed up things are, you can have happy endings.
Did he take the drug? I hate it when people end up developing/taking from each other bad habits, after starting a relationship..