Parenting Teenagers (12-18) Support Group
This community is focused on the joys, challenges and concerns faced by parents of teenagers (12 to 18 year olds). The major areas of child development include: physical development, perception and sensory development, communication and language development, cognitive development, emotional development and social development.
There's another DS board that deals with estranged adult children that you might be interested in.
http://www.dailystrength.org/groups/parents-of-estranged-adult-children/discussions
Good luck with your son. Some kids do come back, some don't. Meanwhile it's pretty hard to deal with.
At some point, you could tell him that you respect his desire for independence and that you want to maintain a relationship between him as a healthy adult able to make decisions and you as his mom. Part of this is that he is struggling.