Water.

I think you are like liquid.

Sometimes you are neutral;

cooling, calm, life-giving.

Sometimes you are bitter;

I feel like spitting you out, but I have to swallow you

-kind of like medicine.

The worst: Sometimes you are acid;

You corrode me

-inside and out;

You inflict pain and leave me scars

-that cannot be healed, forgotten,

even when time passes, 

the reminders of those effects of your acidity 

-stay.

p.s: Sometimes you are the ocean, cool, calm and deep; but deadly as hell.