Iam nothing

I'm 23 years old and live with my father, his wife, and their children. I feel so alienated, lost, and like I don't belong. We don't even eat together or speak except when we have problems. My stepmother has invited the neighbors over for dinner, which she's cooking herself, and they've all started cleaning and preparing the food. Meanwhile, I spend all my time on the phone, as if I don't even live in this house where I don't feel like I belong. I remember when my stepmother invited everyone over, and I sat like a guest next to my grandmother. Afterwards, my grandmother told me she was ashamed of me for not helping my stepmother, even though my stepmother doesn't want me to help. Of course, I don't like pretending to be a normal family in front of people. So today, I decided to act like any other day: I'll go to bed at my usual time, which is the same time as dinner for the guests, and I won't leave my room because I don't see anything worth going out for. Even so, I feel this situation is bad because I know people will be surprised by my absence. I really wish I could leave this house, but unfortunately, I don't know how because I'm unemployed. Without friends and extremely lonely, I think I'm quite pathetic, even though I try to pretend to be strong.