I have a stepson who was on heroin. I don't know all the details because he keeps them to himself. But there was a point where he was essentially homeless, running with a crowd of people who lived in motels off and on. I don't know how he survived. We refused to give him money or rides anymore. He ended up in a shelter here in AZ. He finally got clean. He then moved into a sober living home with other addicts. He then became manager of the sober house. He is an active member of Heroin Anonymous. He chairs meetings, he works a full time job, he saved up and bought a car, he is paying his legal fees, he is saving up to get his own place to live. I believe he has about 16 months clean now. It's been an amazing transformation, and my trust in him is rebuilding from zero to about 90% at this point.
It can be done, people can hit the lowest of lows, end up sick or in jail or homeless, but if they want to live they figure out a way to do it. I hope your nephew turns around. He has to do it himself and want it badly enough to make it happen. It is heartbreaking to watch a young person fall apart. But don't enable him. Don't help him financially unless you are SURE he is totally clean. You can't help feed that heroin monster. Don't listen to the b.s. that comes from an active users mouth. They will throw anything they can think of to get pity and access to the ONE thing that brings them comfort, and that's a shot.