I feel like a spare child even though I'm the full-blooded child

I have an older cousin who grew up with my parents before I was born. She's like their first-born daughter. When I was a kid, I didn't mind my parents being sweet and soft with her. Plus, she's like my older sister even though we're not really close. As I grew older, some people mistook me as her. Most people recognize her as their "child" more than me and even look for her when I'm the one standing with my parents. Some of my father's relatives also mention her in some conversation and how they used to come with her in my dad's hometown before. This cousin of mine is 8 years older than me by the way. I'm currently 17 turning 18 this year and she's almost 25 this year. She's in Angola right now for work. she's been there since I was 15. My parents casually talk with her online. Just right now, I was eating dinner when I told my mom about how scared I am of my future. On the other hand, my father was drinking with his friend while talking. My father happens to mention to his friend that THAT cousin of mine just messaged him. They talked about her as I was opening up to my mom. My mom then ignores my words and goes to my father and joins in their conversation about my cousin. I suddenly felt like my eyes were about to water, but I held it back. As I was fighting the tears that wants to gush out of my eyes so badly, I finished eating and went to the kitchen to put down the dishes in the sink. As I was on my way to my room, a sudden feeling of jealousy and pain attacked me. I kept holding it back because I know it was wrong of me to feel that way, but still, that's what I'm feeling and I want to let it out... But I just can't. I'm now asking myself, how come I only felt this now? It was never an issue to me before, so why does it hurt me now? At this moment, I feel like I'm only being cared and loved because I'm their "daughter" and nothing else. I feel like I'm the spare child even though I'm the one that my mom gave birth to. I feel useless to them. I feel like they think I'm useless because I'm unable to help them. I'm trying to do my best at school. When I tell them about my achievements, they seem to not notice my success. All they see is my mistake. Now, I feel the need to do best in life. To get noticed and for them be proud of me somehow.