Why am I having so many dreams of my ex gf?

We dated for 3 years and have been broken up for about 2. I have dreams about her -more than I would like. I have dreams about the dog we got together too -a mini dachshund. I'm 28 and still brings tear to my eye's when I think about the dog. The ex, fine, we weren't right togther. But the dog, i think about her a lot. Maybe it's my subconscious mourning the loss of the dog an the ex, I don't know. Sometimes i thinks it's odd that I think more about a dog than I think about the ex. I do miss her a great deal...after 2 years. I haven't moved on from either of them it would seem. why? And it can't be b/c of love.