I decided to read this book because someone I was interested in had read it.
Someone I was interested in read this book so I wanted to read it too.
I decided to read this book because the girl I'm interested in has read it.
I decided to read this book because.
この本を読むことにしたのは、
someone I was interested in had read it.
気になる人が読んでいたからです。
Someone I was interested in read this book so
気になる人はこの本を読んでいたから
I wanted to read it too.
私も読みたかった。
"The boy I'm interested in"/"The girl I'm interested in"は自然な「気になる子」になります。