@fffff,
Your English is fine; I definitely understood what you said.
I have to say, I'm kind of with your parents after reading more of the story. You have literally invested going on $10,000 for this guy. And his bad habits, they aren't just bad habits. They are expensive and self-destructive. He doesn't work, either.
He's what we would call here in the US a sponge or a leech. You are only as good as what he can get out of you. I'm sorry, and I know that is really blunt. And this doesn't necessarily mean your parents' choice is so great for you, either. But you are bedazzled by this 'bad boy' who is really no more than a taker, I feel.
From everything you have written, I don't see anything at all lovable about him. Nothing intelligent, generous, caring, thoughtful, hard-working, funny, pleasant, moral, or kind. And if I am mistaken, then please tell me! But from my perspective, I am not seeing any positive qualities whatsoever. And I suspect your parents have a similar vantage point (and keep in mind, I'm probably a lot closer in age to them than to you, although I have no kids).
Anyway, as for the younger not marrying before the elder? I'm really glad that's not the tradition here, as my elder brother got married two years after I did.
Hang in there. I think once you put some distance between yourself and this relationship, you'll begin to get more of a perspective on it.