Why do i get so upset?

I recently moved from england to ireland because i had alot of problems over in england and im only 12 ive had a tough life not knowing who my dad is and everything but before i moved to ireland i had to give my dog away snoopy she was the best thing that ever happened to me i had her for 4 years and it felt like forever but when i look at her in pictures or i hear people talking about her i get upset i really love dogs and i love animals but i am a huge doglover how do i got over this i miss her soo much and i will never be able to forget her and i cant believe my mom gave her away i wouldnt of but it has been such a struggle for me and my mom the last few years anyway. thankyou .