Oh Emma
*HUGGLES* Im so sorry to hear what happened to your little Alfie. I hope that you are doing ok and not coming down to hard on yourself. It sounds as though there must have been something underlying be it a mysterious illness or just old age. You know you never did anything wrong since the other hams made it just fine. You took all the precautions necessary for a long distance travel. I dont think that there was any error in anything you did. And at lest you got him to a vet and did what you could. There probably wasnt any way of knowing or way or predicting this outcome with Alfie.
I hope that you are feeling ok; if you need to vent or anything please do we will all listen and will understand.