Jealous of stepsister?

And although my parents are separated and my mom has had a new boyfriend for 5 years, he also has a little daughter (8) and the problem is that I'm mostly only with my mom with my real sister and we go to 2-3 days every week our dad. He doesn't take part in our life at all or supports us, we never get anything or anything. And my stepsister even gets a Nintendo Switch with my mom, has a tablet and a Nintendo 3ds and and and she has an advent calendar filled with us by my mom herself. That's all nice but it makes me jealous when I think about the fact that I have nothing with my dad and that she gets everything from us, clothes and holidays and money from my grandparents. That's how it should be, but because we don't have that with our dad, I'm totally jealous and angry and sad.

What can I do against it? I do not want that

Envy is an ugly quality. No matter how, you will have to live with it or find another way.

Rather be glad that your stepsister is integrated.

It's totally silly to be so jealous

I can understand you on the one hand, but the little one is 8. Your father obviously doesn't behave like a real papa. But nobody can do anything about it except himself.
It's a shame for you. But do you really want to wish the little one what you have? Or. Not indulging in this just because you don't have it?
You also have to understand your mother, she is the stepmother and of course she wants her non-biological child to feel comfortable in the family.
It would be best to have a conversation between you and your mom, where you tell her how you feel. She probably doesn't even know.
But as soon as she knows what's going on in you, she will respond more to your feelings, I'm very sure of that.

With your (almost) 18 you can't compare yourself to an 8 year old girl.

I'm also sure that your mother has given you and your sister a lot of beautiful things.

You are jealous of everyone. No matter if it is the stepdaughter, friends or vacation.

You are not at peace with yourself. You least appreciate yourself. YOU and your attitude towards yourself is the problem and not the other!

You only see the other's lush green lawn. You can't see how much effort such a wonderful lawn takes and how much care it means.

Maybe you are wondering what the problem is. The problem is not your stepsister, the problem is disappointment with your father.

Don't project the problem and the jealousy onto your stepsister, she can't help it.

Maybe you talk to your father about your feelings… But that probably won't do much good. But now you know why your parents are separated…