I never blamed my parents once. What could they have done to stop it? Absolutely nothing. My dad was there for me when I needed him, helped me through it when I was a kid and still supports me now. He knows that I have days where I think "why me?!" But it's certainly nobody's fault. It's just one of those things. It can be a pain at times but it doesn't stop me doing anything. I managed to go to university and had a great time, I've been travelling, even been skydiving (that was scary!). Yes, I have to think more carefully about meals and yes, being on insulin can cause its issues (mostly it just makes it hard to lose weight) but I live a happy and healthy life. I can honestly say that I have never and will never blame my parents and I am sure that Oscar won't either. I blamed my parents for a lot of other things - I barely tip 5 foot, skin that practically reflects the sunlight, a real inability to cook anything - but never my diabetes.
Don't be so hard on yourself. You're there for Oscar and you'll help him through things. It will get easier, I promise x