The fact that you want to quit smoking is a very positive move forward, the fact that you are seeking help with your PTSD is another step forward in the right direction, you really have to be your own advocate, mental health awareness has a lot to be desired both in UK and USA, I strongly suggest you get in touch with veteran charities who will understand your mind set better, staying with your buddy if you can seems a good idea, even if you cant stay maybe he can help you find a charity.
You were a soldier that means you ARE a soldier that never leaves you! you are a fighter and YOU matter, so one step at at a time, go get better, there is no magic pill or wand that will take away the pain but seeking help is the first step, good luck. we are here when you are ready!