Help writing a song, Please?

I'm writing a song about a person that i used to have a thing with and i thought they were just the coolest person ever. but now they hang out with different people and theyre turning really preppy and annoying-but occassionaly i can see the old person in them. and i wanna write a song bout how frustrating it is, but im having so much trouble coming up with lyrics.. i want to call it chameleon.