Maybe he's acting like this because of his diabetes diagnosis. Maybe he's irritable because of his blood sugar level.
Has he tried a diabetes support group? Maybe one would help him.
Could also be you and he have fallen into a rut as a couple -- look into discovering new activities you can do together; investigate them as a team.
There are many I can suggest: Ballroom dancing, martial arts classes, signing up for coed sports lessons (tennis would be one of them), taking an adult school class together (there are courses that are many and something is sure to interest the both of you) volunteering for a good cause (Literacy Volunteers of America would be a good one; houses of worship always need volunteers and teen programs/kids programs on weekends always can use ressponsible adults.
You can also look into mentoring, teaching adult school classes (do you have a hobby you can teach?) and many others.
He has no right to treat you shoddily and less of a right to treat you with no civility. He needs to stop that treatment immediately; I'd make it clear he's in the wrong.
I don't know what you mean by a lifestyle change --- clarify that, if you would. Do you mean that due to dietary reasons you no longer go to parties and other activities where there will be things on the menu your H can no longer eat in abundance? From what i understand, anything in moderation is fine for a diabetic -- it all has to do with blood sugar and knowing what portion is a sensible one that won't whack out your glucose levels/insulin.