It’s not unusual for a child to rebel a little bit, and in fact, it usually turns out to be healthy. But is this what is happening? From the outside, this is not what I see.
You say he listens to terrible music, with curses and everything. But, he is not really rebellious. He is not standing up and saying: “I’m not interested in a frum lifestyle, which was imposed upon me as long as I was a child, and I am not interested in college either; I think my career is in disco music or in the show business, dirty words included: live with it”. If that were the case, I think supporting such a child would mean a lot, and possibly such a child would remain shomer shabbos and keep kosher and so on, in a secular environment, according to his wishes. But this does not seem to be the case. Plus, your son is a very sweet-hearted child, who feels embarrassed, who as your friend says, deep inside does not care for that music and time-wasting, and who knows why he hangs out with these boys? You assume he is seeking for acceptance, but instead, I suspect he might be *offering* acceptance to those kids. This is a child with a golden heart, and as such, he may be taken advantage of (not necessarily by his friends, who seem to be a little bit disfunctional, but overall, decent people) or simply he may be a victim of unfortunate circumstances. You realize that, due to stupid laws (which, however, exist), he can’t legally have a beer with his friends.