The loss of a not-so-loved one

I knew nothing inside.
Only of your cover
So much was left within
That I never could discover

I knew not of your past
Or the future you had in store
I cared for no problems of yours
Which I'm now sorry for

I gained from you nothing
Not even mistake of an unearned run
You were to me an enemy,
A not-so-loved one

Even though we neither shared this love,
I'm regretting choice made with you,
Which gives me something to write of

We were night and day opposite without a doubt
Though containing so many similarities
Changing what I used to think about

I've got new callous cries
I'm now feeling half undone
New emotions discovered
For a not-so-loved one