I use to be an cocaine and heroin addict. I had been using around twelve for about four to five years, finally managed to get clean, and it's a task that shouldn't be taken lightly.
Addicts don't think about others, it's more of a me, me, and when's the next time I can get my fix thought process, but you have to realize what they're living down. Yes, they can act like it doesn't affect them, but it does, they don't have the strength to actually get clean. Addiction is a terrible disease, and it affects not only you but the ones you love. It's hell to wake up and realize everyday the monster you have become, and it's even harder to change that. Addiction is like a slow form of suicide, some people know they're doing it to themselves, but some don't. They won't get clean because of anything you tell them, and if they do they're bound to use again. Your friend has to learn for them self, and they have to get clean for them self, no one else. They won't happen until they reach the very bottom, and from there find a way either to bury themselves alive, or get clean.
The choice is up to them in the end, and becoming sober isn't easy at all, especially with heroin. Heroin withdrawals are among the worst in my opinion, and that's from personal experience. I would compare it with your bones try to crawl and rip their way out of you skin, never ending nausea, constant vomiting for some. You'll curse and swear the day your mother gave birth to you, and pray for death. Yeah, it's that bad, well I got clean off everything at once. It's best to stay away from heroin, no matter the circumstance, because in the end it's even worse than the beginning. At most, all you can do is support them when they decide to get clean, and once your an addict, you always are. You just have to learn to control you urges and abstain from all drugs period.
Once a cucumber becomes a pickle, and no matter how much that pickle wants to be a cucumber again, it's always going to be a pickle.