I wish you good health and such, and I will pray for you, but it seems to me that you aren't stable, or with only a few troubles. You need to take this seriously. And as for adults having input, a lot of them know a hell of a lot more than you about a hell of a lot of different things. You're cursing people much older and (mostly at least) wiser than you, implying they're all ignorant, making light of very scary threats, acting like you're perfectly fine as long as you get the right kind of drugs, and just generally living in a fantasy land.
I know what it's like to have a crappy childhood (though that phrase covers a lot of territory), and it doesn't just go away by the time you're 17 from a magic pill. If I saw you with this kind of attitude after you fantasized about killing my daughter, I'd tell you to stay away too, and I wouldn't be all that nice about it, and I'd be completely in the right. It's very difficult to tell when people mean stuff like that and when they don't, but those who do very often have given ample (in hindsight) warning, very similar to what you did. People are only right to react to it, and you are only wrong to trivialize it.
You seem to have some deep-rooted problems that the pills are only MASKING, not fixing. They're giving you an opportunity to work on the problems, but they're not making the problems go away. You're not ready to be a husband or a father, though I note that your "everything's fine" attitude may be more due to the happy pills than some serious indication of who you are deep inside. It's impossible to tell over a computer, and I'm no shrink anyway. But you need to look very hard at that issue, and maybe look at getting a different doctor. One who won't tell you you're fine, but help you get better.
If you really love her, you won't blow off threatening to kill her, and you won't so quickly decide that you know more than "damn adults" who have very many more years of experience than you do, and a good percentage of whom probably have your and her best interests at heart. You will do whatever is necessary to make sure you seek out wisdom and become the best man you can be, and then become better than that, and so on throughout your life. VERY few people are ready at 17 to commit to someone, and being abused or neglected is just going to put you behind the pace. You may not be able to gain instant wisdom, but you can at least remember that nobody at your age is as smart as they think they are. Usually, not by a very long way.
Maybe you feel 100% sure that what you did should not be called threatening, but nobody else can be sure, because they can't get in your head (and your head's messed up anyway). They have the right and the responsibility to take this VERY seriously and act accordingly, and so do you.
And yes, I do have a lot of specific real-life experience very relevant to your situation.