The injections are nothing to worry about, there's no syringe type needles or finding veins.
The insulin is administered by a small needle in what looks like a fountain pen, into a bit of fat (belly or bum).
Things will be fine, it's hard to deal with at first, coming to terms with it is almost like a grieving process, but it gets easier and becomes normal. No need to fear, if he looks after himself, there's no reason why he won't live a full life, like a tampon tv advert.
His diet needs to improve and so too will yours (presuming he lives at home with you) - no more ready cook meals, shop pizzas, no more sauce jars. They are crammed with sugar & salt (the healthy lifestyle ones are among the worst). Fresh food prepared by you. Not McDonalds and Subway shite. I'm not being presumtious about your eating habits, just saying. A lot of excercise too. He's young so I'm sure he's active.
Don't fret too much, you've just got to get on with it. This is it for life. Good luck.