Answer:
I can be thin but not fat; in your body but never on your placemat. I'm always better when I'm fresh but you'll never see me in the flesh.
I sit in a corner while travelling around the world.
A young man wants to have me but when he has me he no longer wants me. Blade in hand he attacks me and does his best to remove me. Yet he knows that it is all in vain.
What kind of table can you eat?
If I have it I don't share it. If I share it I don't have it. What is it?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.