In my novel, does the basic plot lend itself well to the theme?

I'm working on a novel, and I'd like to know if the plot seems to lend itself to the theme, and if not what can I do to help it work better?

It's the story of three young adults.

One who's basically living for nothing. He has no plans, no place he’s headed. He’s pretty much a loser. He has potential but he’s too caught up in his own pity party to realize it. He ends up doing some stupid stuff and ends up in jail.

One who's on the same page mentally as the first, but she has to take care of people and it keeps her more grounded in reality. Eventually, after years of therapy and destructive behavior, she manages to move forward bit by bit and make a life for herself.

And the third who is the brother of the first who is desperately trying not to be like him, though in his attempts he ends up more like him than he realised. He ends up killing himself.

The basic theme is that one way or another, you’ve got to deal with it (get your life together), or it will ruin you. Also dealing with the current fad of the fetishization of depression and mental disorders and how that's nothing but destructive.