Life is my enemy.

Sometimes life is too miserable. Life wants to ruin all of your life and plays havoc with all the things you have tried hard to get them. But if you fight in this battle like a soldier you will be the winner. I'm in a real war, but my enemy is only my unthoughtfulness!

~

Life wants to ruin all of your life - this is a difficult phrase, it sounds poetic and the meaning is understandable, but grammatically it isn't so clear. It might be easier to say life wants to ruin everything, or life wants to ruin itself. Maybe just play with a few other ways of saying the same thing and see if you can come up with different phrases that suit the meaning and feeling you are trying to convey.

my enemy is only my unthoughtfulness - this isn't wrong, but be aware of the placement of "only" and how it changes the meaning. "only my unthoughtfulness" makes the "unthoughtfulness" seem less significant, while if you say "my only enemy is my unthoughtfulness", it means that while your only opposition is your unthoughtfulness, it is still significant.

I hope this is clear, you are writing very poetically and sometimes it's difficult to understand the meaning or proper use.