My sister and I trained together, and I know for a fact she ran no farther and no faster than me over the summer or on weekends or whatever. Overall, I trained as hard or harder, but I'd say we did roughly the same amount of work.
She consistently ran one minute per mile faster than me. At least. That's 3 minutes for a 5K. That's the difference between solid contributor on the team (me) and getting written up regularly in the local paper (her).
As others have said, life is definitely not fair. At some point, you get over it. In my case, I learned to be proud of my sister's accomplishments. In high school, I was very discouraged and felt hard work made no difference. However, I realize now that's wrong.
Just by running around 40 mpw, I run a 5K about 5 minutes faster than on minimal training. That's huge. I'm usually in the top 5% for my gender in races, sometimes even in the top 1%. And it makes me happy to see my consistent training pay off.
Don't worry about your teammate, but yes, understand that if you weren't born with talent, you won't be a star. But running contributes to physical and mental health and can bring great joy even if you get beaten by more talented people. Your teammate will also get beaten by people more talented than him, even if he starts working hard and never skips practice.