Hi Raptu and welcome to the forum.
I am sorry to hear about your son. You may find some answers to your questions in the Carer's information section
http://www.ptsdforum.org/forum43.html. Being a Carer of someone with PTSD is an ongoing learning experience and I hope by reading here you can find some insight. Being armed with knowledge is fundamental to finding an understanding of how you can assist.
Feel free to share more of your son's situation so others may be able to contribute with their experiences which may be helpful.
Once again, welcome and I look forward to talking to you on the forum.