My heart breaks for you. I had to have my first baby put down. He was 1mth shy of his 12th birthday. He was put down on the 20th of March 3 years ago, 1 week before my birthday
I couldn't watch him be put down, I was a bawling wreck. However, I did feel his spirit leave the vet room when he passed on. The room felt lighter and happier. I miss him immensly.
We have a "shrine" set up at my parents house for him - we had an oil painting done of him when he was about 7, and that sits with his ashes in his wooden box with his favourite toy and collar and lead in his ashes box (it's glassed case but ashes are behind wood so you don't see them).
I have other babies now, but I still credit him for making me the dog-crazy person I am today. My heart aches every time I think about him 3.5yrs on. Remember the good times, that's all you can do. Bawl your eyes out if you have to and don't let anyone tell you to get over it. Your baby is your baby; and they love you no matter what, so they deserve to be mourned properly.