how old is too old to sleep with your parents.
Can you stay with him until he is asleep, then move back to your own room? Or let him drift to sleep to some soft music? I am still putting my 6 and 9 yr old to sleep every night - as in until they fall asleep - before moving back to my own room. I was very prone to nightmares and night terrors as a child and that translated to insomnia as I got older. Sleep is simply terrifying.
DS1 goes through phases when he gets nightmares and needs the assurance of an adult. I am a very light sleeper and am generally at the bedside quickly. I can usually just pat him back to sleep within 5 min so it is not so very bad.
Your son is not too old to want company in (for him) hard times.
Your husband's comments are not helpful, no matter what the viewpoint on this situation is. Hopefully he is not saying such things in front of his son. If he disagrees, he can just say, "I know you (he) can handle it. You're big enough. It will pass." I'm sensing your husband is feeling powerless in this-- obviously you are doing what he doesn't want anyway.
Your son *is* old enough to talk with about this with you. Together you can find a workable solution. Personally, I would ask whether he might want company at some point during the night as you are putting him to bed instead of waiting for that vulnerable moment. If he says "yes" then decide that he can come get you to do X, and try not to wake up everybody. Make sure he knows he doesn't have to cry in bed, that if he wants he can quietly tiptoe and come get you. He *is* big enough to do that.
Plenty of adults don't like to sleep alone. And it's not considered a problem with them. I mean, I like sleeping next to my husband. It's nice to just have him there, and I like snuggling. I don't think that means I'm stunted, or a baby.
What he will get better at is handling sleeping alone. I don't cry if I'm alone. But that just comes with maturity, and that develops naturally at each person's own pace.
I think the PPs have good ideas about how to handle the specifics of your situation. I hope you find a solution that makes your kid feel safe and works for your family.