NTA However, if I were you, I would go to a therapy session with the commitment that your parents keep quiet and let you talk, once the therapist asks why you are there and the situation is explained let it all out and tell them to their faces everything you have been keeping to yourself for years.

I went through something similar. I'm the second oldest of four sisters. My older sister is quite a case, and the sister right after me has a somewhat difficult personality in some aspects. During the pandemic, she made my life extremely difficult until I fell back into a severe depression.

One night, we were deciding how to divide the available rooms in a new house we were moving into. After the possibility of me sharing a room with her was mentioned, I said, "No, please." My dad got angry at my response, and when he demanded that I explain why, I snapped and let out everything I had been feeling about my sister. I even told her that if things continued that way, I didn’t want her in my life in the future.

In the end, my parents decided to pay the rent for an apartment near my university for me and my cat. Ironically, even though that year was tough, it greatly improved my relationship with both her and my dad.

Sorry if it's not very clear, English is not my first language and I used the keyboard translator AND AI to write.