I had to practice saying "My husband has ALS". I did it in the car, by myself, and it took a LOT of effort. I practiced until i could say it out loud without falling apart.
We all deal differently. Try t focus on the life he has left instead of what he and you are losing. Otherwise, you will waste the time you have. I wouldn't assume to tell you not to grieve now, but once the initial shock wears off (and that takes time), get on with making memories and helping him live with disease at each stage.
My heart goes out to you. I have two stepdaughters, now in their 30's (almost 40) who lost their mother when they were 12 and 14. My two sons have become the men they are because of my husband. The hardest thing I've ever done was tell the four of them that he has ALS. We were unable to get them all together before one deployed, so I set up a group skype. I made sure the girls were together. I almost couldn't get the words out, and I saw them googling ALS as soon as the letters passed my lips. I could see the realization hit them, and it wa devastating. They have all four stepped in in their own ways to help. They are closer to him now than they have ever been. Nothing makes him happier than interacting with them and our grandchilden.
Help your hero do this with grace
Much love to you