Your post sounds exactly like what I am going through, 1 year of being together never any problems then he started getting depressed around Veterans day. After that it was one stressful thing after another that piled up then one day he told me he needed space. I was so confused, like you I didn't know anything about ptsd, I was heartbroken and felt abandoned. Although he told me he loved me and it had nothing to do with me I still felt like it did. He said he had too much going on in his head and he needed space to sort things out. A week into his isolation I couldn't take it anymore and I called him (again before I knew anything about ptsd). He was very cold towards me and he said that he missed me but other than that he couldn't feel anything, his head was spinning, and if I didn't give him the space he needed it would push him away more. I have not heard from or contacted him since, that was a little over a week ago and it has been 2 weeks since I have seen him. The only things that have gotten me through and able to function are the stories and support from everyone here, and learning more about ptsd and knowing that this is normal and I'm not alone. I also started seeing a therapist to help me cope too. The only advise i can give is what i myself am doing...read the forums, learn all you can, be patient, and just have faith that he will be back and you can work things out. I hope everything works out for you.
Welcome to the forum!