My hubby has a violently abusive past, and also struggles with nightmares and thrashing in his sleep. I can definitely empathize with that portion of it. And while he's come a long, long way, he still struggles with feelings of inadequacy and insecurity. I wouldn't be surprised at all if he'd had PTSD at some point in his life.
I know you said your hubby had been through therapy in the past. Did he stop it at some point because he felt he was "recovered"? If he's still dealing with paranoia and social anxiety, maybe he could use some more support from the outside?
What about you? Have you ever been part of a support group for relatives of those with PTSD?
How does he usually respond when you counter his fears? Does he immediately see that you're right and he's wrong? Does it help to point out that his thinking is irrational? I'm asking because a lot of times, when someone is under anxiety like that, rather than focus on the manifestation (he's afraid someone is looking at him funny), it's smarter to focus on the cause (he's experiencing anxiety for whatever reason, and it probably has nothing to do with the person he thinks is staring at him). I have a TON of experience with anxiety issues... not PTSD... but generalized anxiety, panic attacks, you name it. It can manifest in countless ways, but getting to the core of WHY I'm feeling anxious to begin with, is a lot more constructive than focusing on whatever phobia is currently the focal point of my anxieties.
I don't recall if you've ever said, but is his PTSD from being in the military or from some other cause?