I am sorry for your loss mate.
Can't really help you though.
I did some googling and like I see it what he's undergoing is quite normal. His loss was very recent and his reactions are normal.
"From ages 9 to 11, children come to understand that death is inevitable, even for them. However, children in these age ranges may still feel somewhat responsible for the pet's death, thinking their beloved pet may not have died if only they'd taken her for more dog walks or kept the water bowl full. So called 'magical thinking' and they may believe that their own thoughts have somehow led to something bad happening to
their loved one."
Things to help:
Talking
Talking to your child in an open and honest way about the death of their pet is very important. This way, your child is more likely to feel that they can trust you and talk to you about their feelings if they need to.Talk to your child in a caring and compassionate way and let them know that it is ok for them to feel sad, angry or confused about the death of their pet. Let your child know that you are there to answer their questions in an open and honest way. Let them know that you also feel sad or upset that their pet has died, but that these feelings will pass and the normal routines of life will carry on.
Supporting
It is important for your child to know that you are there to support them through the difficult emotions that may arise when they are grieving the loss of a pet. Provide them with physical comfort, such as a cuddle, if they will accept it. Also give them the time and space to ask questions and talk to you about their feelings. Remember that strong emotions may come and go in waves and may last over the days, weeks and sometimes months to come.
Remembering
It can be very comforting for children to have some way to remember the pet they have lost. This may be by having a photo of their pet, doing a drawing of their pet, or having a ceremony at home to say goodbye. All of these activities can help to acknowledge the important role the pet has had in your child’s life and that they are no longer there.
Thanks very much mate.
We're doing quite a lot of those things for him naturally.
He's blaming himself, even though he wasn't there when it happened. As he believes if he would've been there it wouldn't have happened - the dog inexplicably ran across a main road for no reason at all.
I'm keeping him constantly busy, by having his friends here after school, so he's not thinking about it as much.
Thanks for the advice x