About "as" My sister asked me for a loan but I refused as she didn't pay me back last time.---------Can I use "because" instead of "as" in this sentence? How to use "as" correctly?

About 'as' My sister asked me for a loan but I refused as she didn't pay me back last time.---------Can I use "because" instead of "as" in this sentence? How to use "as" correctly?

My Dream When I was a child I was obsessed with football(Not American Football). From then on I play it everyday and decided to be a football player. But my parents against me to become a football player because of my poor health. I had to give up my dream when I was 14 years old. Although I gave up my dream of becoming a football player, I didn't give up to play it. I spent most of spare time to playing football. Football not only to bring me happy also can let me become strong. I love football and if there is an afterlife I want to be a football player.

First notebook entry: Introducing myself Hi, everyone. My name is David from China. I am Chinese-Korean and my native language is Korean. I can also speak Chinese. I want to make friends from all over the world and improve my English. If you are interest in Korean or Chinese I can also teach you.Thanks for your concern and kindly give me your advice.