Where's The Man I Used To Know?

The man you used to know
Is lost somewhere in my head
The things I used to feel
For you are lost somewhere on our bed

Forget all those love words
I said yesterday, they're untrue now
But yesterday I was so sure
I changed and I don't know why or how

Can you figure this out?
Can you figure this out?

If you can, if you can
Explain me now
Explain me now