Carol,
sorry you had to find us, but welcome to you. I think you will find support and respite here.
Please tell us a bit about your son, age, history, current issues. If you think you will be here for a while (and many of us are, since our kids' issues and their impact on us don't go away), fill out your signature a little more to help us identify you on different threads. My son is also homeless, living under a bridge in fact, and has been for two years. He is only about 1/2 mile away from me. He doen't want to live with me, or with his dad. We did all we could to support him...therapy, rehab, therapeutic boarding school, wilderness treatment centers, psychiatric hospitalizations, even went to visit him when he was living with Occupy Wall Street for several months (before he got hospitalized at Bellevue for 6 weeks.). He is, as your son, also a panhandler...I sometimes pass him on my way to work.
So yes, we can understand where you are coming from. Yes it hurts the heart. Yes it is hard or even impossible to understand.
Others will come along and comment, but please tell us more if you feel like it.
Echo