Wistful, Jim's got it right. Focus on what you can do, not what you can't. Take pride in any successes and confidence will start to grow and spread to other areas of your life.
I must say that your post doesn't really gel for me. You say you are intelligent but later say there's a lack of intelligence. Which is it? You chose to drop out so it wasn't an academic failure was it? It was your choice and now who do you blame? It can only be yourself as you can, at any time, go do the schooling you need. It's your coice, every single time Wistful.
You say you got engaged and will be married. If you're so repulsive and dumb how on earth did that happen? Young ladies don't come to the door looking for a fiance so you went out and met her, and charmed her. So tell me, what is wrong with that? You say you look down on other people. Why? What have you got to be condescending about? You've just run yourself down dreadfully and now you say you look down on others? This is why it doesn't gel to me. You detest yourself, apparently, but then rate yourself higher than any others. Again, which is it? You're better or worse than others. Again, you choose.
Then there's the issue of depression. Do you have it or not? it sounds like you haven't even seen a doctor yet you dismiss any treatment as you "don't see any point in it". How would you know? You're a kid and haven't lived much of life yet. I really don't see that much suffering in your life as you've written it. All I read is you dropped out of school and can't be bothered with trying or getting help. That's not suffering, that's choice, yours.
You say you want to be a writer. Well, sorry but high school dropouts don't have the vocabulary to write good material and likely lack the ability to plan and develop a plot as well. This is what education is about. Giving you skills so again, you choose. Try writing now and see how good it is. What would you write about? You haven't much life experience to draw on really so where is the "real feel" going to come from? In your post you try to demonstrate your writing ability but really all you achieve is length. I mean, "Punch and chips"? Really? If you're going to use that type of line it is always "beer and chips". Punch and chips is not something anyone will identify with. It jarred when I read it and knew you were trying for a colourful, amusing expression. Here's one, "Like a rat up a drainpipe". See? That's real and it simply means fast. What does punch and chips mean?
Writing isn't about elongating the story with superflous statements like that which people will reject. It's about being concise and precise using descriptions where it's relevant to the story. Many do use so many similes and paint so many pictures I know. But does anyone actually read all that stuff? Or do they look for the plot and put the book down cos they can't find one. Not a personal attack, some constructive criticism.
Please see a doctor, get your education and defer your marriage until you have finished high school. You don't like men or your girl's father. Have you though how he feels about a high school dropout as his daughter's husband? As a father I can tell you. But you already know.
Look after yourself, get up and act, help yourself as no one else will.