My dog died a little over 11 months ago and I still dream about her sometimes. Less than a week ago I woke up at 5 AM crying like a baby because I miss her so much.
Advice: spend as much time with him as you can. Pamper him, walk him, do everything you can think of before it's too late. I think I did a pretty good job with my dog (we gave her a whole steak, walked her in our old neighborhood and other places she loved, took hundreds of photos/videos, everything). Hell, the night before she passed I had a long "talk" with her in the car, which sounds silly but it made me feel better.
Treat the time you have now like it's gold. Despite all of the stuff I did, I still wish I could've made up with my dog (I called her names and teased her as a kid a long time ago).
Don't be afraid to tell people what you're sad about; a dog is a living, breathing family member and they're still very important. I don't know your whole situation but I assume you're very close to him since you spend lots of time at home.
To be blunt: your life is going to be very empty once it does happen. Something is going to feel like it's missing. It'll feel like the air itself is noxious, not with poison but with grief and sorrow. I'm not a good writer but it'll be hard.