I am so proud, and ashamed of my teenage son... What can I do?

I left my husband when our child was only 4... Now he is sixteen, I have seen him again, and he has such a different lifestyle than I had imagined. Some of it is good, but some of it I can't even bare. He is going to college at 16, volunteers, has an internship and a job, is very healthy between sports and a good diet, and is a very skilled artist, alongside so many other amazing things. But he is also throwing it all away! He used to do real sports like tennis and basketball, but he has never done a really real sport like baseball or football, and has taken on the brutality of martial arts and swordplay, and archery, like he is readying to kill something. He call them the sports of a craftsman, but come on, he is hitting things and using knives. To add to that, he is a stupid goth/emo kid. He says they are different, he is just goth, and that it is a lifestyle that found and fit him, and he has been so for four years, and doesn't intend to let it stop. I thought it was a phase, but four years? And a LIFESTYLE? Finally, he no longer embraces Christianity, but rather has taken up being agnostic (which I still don't really get). What can I do?