It won't be long before I go mad

I don't even know where to start from my life's so fuckd up right now. Firstly I have a cousin who lives with us because her parents left her. I didn't have any problem with her before but after my parents have adopted her , she changed now, she is jealous of me from first day till today she uses my things without even bothering asking to me not only use but destroy it. At first I was upset and explained her to not touch my things but she doesn't listen starts arguing with me and hitting me. I understand because of her past she has became like this, I thought she will change living with our family which is very quiet and we don't shout much but she changed us, my father and mother who never screamed at me, scolded me because of her. I a introvert , soft spoken person has become a depressed, loud and angry. Before her i used to be very good in studies but after her I am struggling to pass , affecting my mental health even more next, are my parents who don't even understand me expects me to give everything to my sister because I am the elder one . They're not much invested in me on how I study and didn't even let me go to tution because they have money for only one of us so my sister goes to tution and I just self study like she's in V , I am in X but the irony they tell me that I am their only support for their old age and when my results came i got average marks they scolded "WHAT YOUS STUDY IN SCHOOL ALWAS WASTING TIME ON PHONE". mostly i only watch educational videos My hobbies were writing painting and editing were stopped all my strengths are gone Boards are near and I want to score good marks so I can leave my home and go far to study but with this kind of situation i dont know how I will give boards Thanks for reading my rant❤️‍🩹 it feels good to pour all my heart out even if it is to strangers.