Heroin Addiction Support Group

I just learned that my brother is a heroin addict. He admitted to our parents that he has been using for 2 months but we all think it's way longer. He has a history of lying even when he's sober. After hearing the news from an outside source, I called my brother to hear what was going on. He was so messed up he couldn't even put 2 sentences together to equal a conversation. Nothing he said made any sense at all. When I asked him about his beautiful little girl that was born 3 weeks ago, all he had to say was that she's at his wife's mom's house. He didn't even seem to care about her. His wife was just recently arrested for kiting checks on 4 different bank accounts, so we think she may be using too. We're really hoping that she didn't use anything during the pregnancy but we can't be sure of anything. I've already lost a cousin to heroin 4 years ago and I'm so scared to lose a brother. What I don't understand the most is why heroin of all things??? Someone please help me understand what makes these choices get made.