Hi, and thanks for writing to me.
It sounds to me that your old dog was really important to you in the early part of your life. Just reading your letter gives me some idea of how much you loved her, and because you'd known her all your early life, she was part f everything you did as you were growing up. It makes sense to me that you'd think about her in the same way as you'd think of a person who'd died, she was so important to you.
It's ok to have a cry about people and pets that we no longer have in our lives, and just because other people in your family don't cry doesn't mean that your feelings are wrong.
Crying after so long shows that you still feel some pain about what happened, crying is normal, and something everyone does when they are trying to cope with feelings.
I really think it would be good if you could talk over your feelings with someone, and perhaps that could be in a call to ChildLine? The counsellors there will listen to you and talk about how things are for you - could you give that a try? The number is 0800 1111, calls are free and the lines are open all the time.
You can also chat online to a counsellor, just sign up for a ChildLine account.
I hope you'll try talking to someone at ChildLine.
Take care
Sam