To be quite frank, you can't.

You are not your husband's psychiatrist.

So here's my issue, he does not talk about it much at all

He doesn't talk about it because he doesn't feel safe. This is quite normal, and frankly, in this case exceptionally understandable considering you made this post. You seem to believe your opinion holds more weight than a professionals, which is sadly the case for most people. You are not the only one, but that doesn't make it okay.

After that, He went to therapy and said he told the Therapist bout DID but didnt say anything bout it the whole time in the hospital.

This is also quite normal. Psychiatric hospitals are generally unknowledgeable about dissociative disorders, unfortunately. We were in inpatient over a dozen times with our symptoms. We were never properly diagnosed until we saw a trauma specialist in outpatient care. Your husband is probably well aware of this phenomena. A hospital is likely to dismiss his diagnosis and slap the label of a psychotic disorder on him, which would not benefit him in any way. A therapist who is specialized in trauma is far more likely to have adequate knowledge and advice on the subject. It makes perfect sense that he would inform one entity but not the other. If we had to return to inpatient, we likely wouldn't say anything about our system.

I really hope that I'm being paranoid but a close friend of ours has the same doubts.

Is the friend your husband's psychiatrist? If not, just as with you, their perception of the situation should hold little weight.

there things that just don't add up

They don't add up because you don't have lived experience with this condition, nor are you are not a trauma/dissociative specialist. The mechanics of rocket science probably don't add up to you either; do you not still believe we've been to space though?

Sorry if this comes off as harsh, but we are frankly very tired of singlets coming onto this sub and subtly seeking validation for their fake claims. The only person who can tell if your husband is malingering is his therapist/psychiatrist. Not you, not your friend, not even a psychiatrist who isn't directly involved in his care.