It's because

I liked looking at you
Wish it was something I could always do
Sitting next to you made me calm
Not seeing you felt like loosing an arm
It's because I used to walk on the road
Where one rail was yours
And the other was mine
The simple nature of yours
Had made me blind
Now the train has to turn
I will lose my rail
but you'll have two
It's not something that I want
but must do...