My mom and aunts drove down to Primary Children's a few hours ago to see my cousin's son, because he wasn't doing well. I passed on going.
I just found out he died while they were there...

No such thing as a life without regrets

I understand. I had the chance to go with my mother to be with my grandmother as she died. I stayed home because I was in denial. I didn't think she'd go so soon. But she did.

I just...
How does a healthy, active, 16 year old kid for of a sinus infection...?

Sometimes the body can't handle certain things, or maybe there was an underlying illness the doctors couldn't pinpoint, many reasons that don't change the outcome. Either way you didn't know it was going to happen, you shouldn't feel guilty about not being able to predict the future. I'm sorry for your loss but don't add to the pain of a loved one passing by placing guilt on your shoulders.