>...apparently I'm destined to slave away at C++ legacy code all my life. Which is really what depresses me.
Well, there's another difficult lesson there - there's no such thing as 'destiny', however much it may feel that way sometimes. Many people willingly or unwillingly follow the random wind of fate and think of it as destiny but it is just the nature of life that 'things happen'.
The good news is that knowing this frees you up somewhat - your life is yours to control. The trick is working out what you want (and you apparently have some idea now, more than most 20 year-olds) and then what steps you need to take to get there.
Some suggestions:
1) Beware the myth of the overnight success - getting where you want to go in life almost always involves many incremental steps and lots of work, yet we are surrounded by stories of companies and individuals who hit the jackpot and found success instantly. In reality that almost never happens and what we usually don't hear about are the years of trial-and-error and effort that went into building that success.
2) If C++ is your strength, perhaps you could find a way to use that to finance the transition? In the short-term, another coding job could give you the money to pay for art/design training and help you move into the career you really want. The key here is to get the best out of your free time. This is one way to avoid the 'fate' that you fear - use the lemons you have to make the lemonade you want.
3) As some other people have said, tell us what you can do and what you've been working on, and perhaps someone here will be able to offer you some freelance work to help with your cashflow.
Sorry to hear that your Dad and your friends are being so unhelpful. All I can offer there is one of the great 'aha!' moments in my life so far - when people are being persistently unpleasant to you, it almost always reflects insecurities that they hold about themselves, rather than something you've done wrong per se. You've come to a difficult point in your life and throwing blame or sarcasm around does nothing to change that, only appeases their demons for a short while. I don't know if that helps at all but it helped me to realise that I wasn't to blame for other peoples' anger - we all make mistakes and have difficult times but the constructive thing to do is to find a way deal with them and move forward, not wallow in the problems we perceive others have visited upon us (I'm referring still to your father and friends, not to you).
Enough rambling; I hope that helps and wish you the best of luck in the future.