First of all, contrary to what military ads and American culture try to tell you, there are many paths to "grow[ing] up and get[ting] confident and strong" besides picking up a gun and being sent to far-flung lands to secure access to resources that the multinational corporations desperately want.
Have you considered Teach for America, the Peace Corps, or another such service-based group?
If you wish to do something more physical, consider taking a semester-long NOLS course. They offer financial aid if money is a factor (they're expensive but you learn GREAT leadership skills - I've used what I learned in my NOLS courses in many other areas of life). www.nols.edu
Here's a page run by a Quaker group about alternatives to military service:http://afsc.org/resource/alternatives-military-service
And here's one more site that lists a bunch of alternatives depending on what you're looking to do:http://www.nyclu.org/milrec/alternatives
I know Vets for Peace has something out there but I couldn't find a good quick guide on their page like the NYCLU page has.
Good luck, and congrats on at least one piece of "growing up" that you've already done - you've looked at your own conflicted feelings about your friend's enlistment, owned them, and expressed them. A lot of guys NEVER get that grown up.