The first few months after diagnosis are horrible. I remember being both upset and very angry. I was really worried people would treat me differently. Some did. Every time I did or said something they'd say "Is it your blood sugar?" Like I was no longer me any more. It drove me mad.
Have you asked your husband what you could do to help? What his concerns are? Sometimes it's little things that get to you. If you know exactly what your husband is worrying about or what upsets or annoys him, you can try to help.
I don't know about your lifestyle, but is there a favourite thing you coukd do, something from before diagnosis, that would emphasise to your husband that he's still the same person, and life can be the same, apart from the added nuisance of diabetes. It's an extra, something stuck on to the outside of you. It's a bl**dy nuisance, but tell him he can get through this. Don't give in. Think of it as an extra piece of luggage he has to carry.
If it's his blood sugars he's worrying about, please tell him that nobody's perfect. Even people who've had diabetes for years get highs and lows. That's the nature of the beast.
I'm sorry he's feeling so down. There's no magic answer. Time will help. Having fun, relaxing with friends can help, anything he enjoys. Don't undeestimate how psychologically affecting it is. It's something that has to be with you 24/7. It can be a battle to get on top of it mentally, but it does happen as life moves on. I found reading about other people with diabetes helped, as I didn't feel so alone.
Best wishes to you both. It will get better.