"
And yeah, I let you use me from the day that we first met
But I'm not done yet, falling for your
Fool's gold
This part explains how the singer let the girl use him because he was so deeply in love with her. The girl is compared to fool's gold which is a mineral usually mistaken with gold. The singer explains how he has mistaken the girl for something precious (gold) when she is actually just using him. All the singer wants to say is that he fell in love with fool's gold taking it by mistake for gold.