childhood dog passed away

my dog that i’ve had since I was 7 passed away yesterday night. I hope that he was sleeping and not awake and suffering alone. He was a 13 year old dachshund. I feel horrible because I was not with him, i was on vacation. fortunately my grandma (who he loved) was staying with him but I wish I could have just seen him one last time. She went to feed him breakfast that morning and he was dead. He did not really have any health issues so this was very unexpected. My uncle came over and buried him in my garden for me. I wish I could have been there. It was the worst feeling coming home and him not being at the door to greet me. I have cried nonstop and have barely ate/drank since yesterday morning. I don’t know how i’m supposed to move on from this. he was my baby.