The dog that I grew up with died last summer and now I feel like he never even existed, is that normal?

I am 18 and my dog who I grew up with had to be put down last summer of old age. He was like my best friend, I loved him more than anything he was family but for some reason when we put him down I did dent cry that much and i started to subconsciously feel this strange feeling, like he never existed, it's like duh I know he exsisted! But the feeling is almost like the events in life with him in it did dent happen or something. And when I see pictures or videos with me and him Its the strangest feeling..I don't really know how to explain it...just like that memory with him never happend. And its making me so sad! I want vivid memories of my dog! He was my favorite thing in the world! Why do all my memories seem like a dream?