Is the following sentence correct in usage,please?

Question

but,i think that's because i have been sitting in the car of my friend friend that's why my back hearts like that

Answer 1

its wrong

it should be:

but, i think that's because i've been sitting in my friend's car, that's why my back hurts like that

Answer 2

no, sorry.

Not sure why you start with "but"--it's not ideal but I'll accept it.

But, I think that my back hurts like that because I have been sitting in my friend's friend's car.

I guess that's what you mean.