She was with us ever since I can remember. I have two brothers from my real mom and three younger siblings from her (step mom). We grew to love her, my brothers and I, but lately we found out in one incident that she was just doing all these 'motherly' tasks as an obligation because she married our father. It wasn't direct but I'm pretty sure that it was what she meant. I also remember that when we were young, we were rarely given the things that we want (toys, clothes etc) because she doesn't want to. Said it was a waste of money. But her children gets everything, toys, clothes, gadgets. We are not jealous because we are way past that. But they began to be brats. I love them but I don't like their attitude. I'm a sensitive person but I don't like arguments and fights. I just want to finish college (2 years more), get a nice job and move away from home. Does this make me a terrible person? What should I do to make my stay here at home enjoyable?

No, it doesn't make you a terrible person, and it's very common, often with much worse distinctions between natural and step children.
Or it happens with birth parents. My mother resented everything about her marriage, and that extended to her children.
You are getting college paid for, presumably, plus living at home? That counts a lot.. you could look into living in a dorm or a cheap shared apartment and borrowing the money to do so.
Or you could just immerse yourself in getting good grades and being glad you aren't the same as her kids. See if you can graduate early by going to summer classes.

I'm so glad that you do love your step mom because some kids never love their step mom and never appreciate what the step mom did. I have a 14 years old step daughter. I do love her as my own and taking good care of her for everything but she never appreciates me. All she does is making her father get into the fight with me. I don't have a children and she is the only one I been taking care of. Due to my husband unstable budget, I didn't buy a lot of clothes or toys for her but I do buy all of her necessities. To me, it's hard to taking care of step kids which is not my own because they don't love me and don't appreciate whatever I do. So when I read this post, it was surprised to me and I am so glad that you do appreciate and love your step mom.