W/O/W,I am seeing a lot of people here discussing the matter of going off the derech,but nobody seems to come with an idea that might actually work; we see all the old show your unconditional love,show the beauty of yiddishkeit,etc. I am not saying that they are not important,but let’s face it,have they had any results until now?
I want to suggest one thing that might be controversial,but I suggest it might be worth a try. I am by no means a professional therapist or psychologist,just a young adult who likes psychology. I suggest you buy your son a camera and give it to him to take photos. Why? You mentioned your son is a very private person and it’s hard to talk to him about his emotions,he is an introvert. Introvert usually express themselves very poor and by giving him a camera,you would encourage him to get creative and express himself. You mentioned he seems angry. Art is a beautiful way of expressing your emotions. There is actually art therapy. You might also buy him an inspiring photo book about something like landscape photography,that can inspire his emotions to be expressed. You don’t need to spend a lot of money on this,a decent camera can be found on B&H Photo and Video for like a hundred to two hundred dollars and for a book something around 20-30 dollars.
If you think that is too expensive,try something else that is art related,like painting,or a video camera for him to make his own movies. Just encourage him to get creative and express himself.