I hope you're finding peace with what happened. Losing a pet sucks.
I will say it's more common than you think. Pets obviously can't communicate explicitly what they're feeling, and so something they've been fighting might come as a surprise. Furthermore, the older the pet, the more likely they'll develop health conditions. Hell, even humans sometimes don't realize they have cancer until it's too late to treat. What I do hope is that your dog lived a happy and fulfilling life and that they passed peacefully.
As for moving on -- like the others have said, everyone moves on at their own pace, but no one moves on completely -- we just grow as people. My dad is nearing 60 and still talks about his childhood dog and how much he misses him, and I imagine I'll be the same when my 12 year-old schnauzer passes too. What helps people ease their pain is the memories they've had, and that always includes pets too. Grief helps us remember who and what it is that we love.