Marriage without sex....

So, I need some advice. Lately I keep having this overwhelming insecurity in my marriage. my husband is a vet with PTSD so we have been through a LOT. I know he would never cheat on me... but I do get scared of him leaving. I've picked up some secondary PTSD from the relationship because of certain situations that came out while he was going through the worst of it (so far.) I keep getting some mixed signals and I'm driving myself crazy trying to "save my marriage" or fix a problem that he swears isn't even there. Let me explain:

So we don't really have sex anymore. We've been married for almost 3 years, and we have been together for about 5. When we first got together everything was great. Emotionally, physically, and mostly mentally. We got pregnant and I had our son. We got married about 5 months after (already had plans for it). But a few months after our son turned one, my husband quit having sex with me. That's also about the time he started escalating with the PTSD and having some serious problems so I always called it up to that. So did he.... but then it continued.

Fast forward two years and he's doing SO much better. But now we're going 3-6 months in between having sex. But I know for a fact he'll watch porn and get off. It's made me super insecure. He's given me so many excuses and we've "worked through it." Which means we had sex for like 2 weeks and then it would fall off again. I know he's not cheating. But it makes me feel so inadequate. Right now the popular answer from his is that if I'm not available (if I'm at work... and I do work 60-70 hour weeks) that he'll just take care of it... but when we do have some time together he's always just "too tired". I don't understand. But now I'm insecure and I can't shake it, and I'm not sure what to do to improve this? Am I crazy or...?