The phoenix is not a legend, it can be you
Seeing you asking about advice and seeing this strength, the desire of yours to stop this before it gets worse and deeper shows me how much you are strong-willed and how your heart is shining with hope. Yes, you may think about how this is possible, but I know what I say, hope.
Start from there. If you were convinced that the heart is all dark, you wouldn't have asked for help. So, keep it up and don't give up on these ideas.
Fist, I think you should understand and admit the situation you are in very well. This is the hardest part but you already did it. You see? you are doing great.
Second, look for counterexamples. Your thoughts tell you that everything is dark, the world is doomed and done, but, hey, how can that be true, when you find a lot of strangers writing hundreds of words to advice you and help you. Look around you, and you will see how much there are nice things. They sometimes just don't show up a lot because bad things tend to get our attention faster.
Third, you have to know that, for example, when your dad or mother or anyone beloved worry about you or care bout you, that's not pity, that's love and caring, and this is one of the examples of the beautiful things in our world. So don't be afraid of this side because you wouldn't open up to someone who isn't trustworthy. But yes, of course, this is not easy, always. So why don't you use writing? Not just one paragraph to explain your feelings, but make a collection, some poems, and some paragraphs and give it to your parents. If they read it, they will see what you feel and what you think, and that's a good start.
After that, things hopefully will become easier. When your parents understand everything well, they will know how to act, especially that they know you. And in ultimate cases, you may see the advice of a professional person. But I think that you will be fine before that.
Fourth, use writing not just for that but also to release these bad ideas and feelings. It can be drawing too. Let it be like it comes naturally, even they turned t be te darkest drawings or writing. If they go out, they are no longer in your head. They would be lost between your pen and papers, and that's what they deserve, to leave you alone and become a beautiful creation of yours. That's how we turn our problems into a push forward. I had an experience with this. I remember, a long time ago, I had something that annoyed me. I was little then. I remember that I was crying and I was so angry. I took a paper and made two or three drawings. It was a dark forest with trees having opened mouths and eyes, haha. But I remember well how much I was surprised when I calmed down totally after doing that.
Fifth, read inspirational poems, writings, real stories of people who beat such situations. So you get more ideas, more reliable devices, and a beautiful push of hope.