I’m very glad you wrote. Feeling always in second place must be very painful. It sounds to me like you have been such a good kid, your mother doesn’t worry about you. She knows you will be okay. But she apparently has major worries about your sister. Is it possible that your sister isn’t as smart as you are or that she has some other problem that worries your mom?
It’s an unfortunate truth that a kid who seems to be doing fine often gets kind of taken for granted in a family, especially when another kid seems to need special attention to be even mostly okay.
You seem to be taking your frustration out only on your sister. It is your relationship with your mother that I’m more concerned about. She may be quite unaware of how you are feeling since you work so hard to be the “ideal” kid. I wonder what would happen if you had an honest discussion with her about how you do need some of her attention — and even praise now and then. If you can find a way to talk to her calmly about it, you may be surprised at how clueless she has been about how you feel. The two of you might be able to work out some special times in each week for just the two of you.
If you and your mom can work out a more friendly relationship, I think you will find much of your anger at your sister will evaporate.
You didn’t mention your dad. If he is in the picture, it may be possible to form a special bond with him while you work on things with your mother.
I wish you well,