Boy with strange body

The book is about a boy whose body is different, his interior body is much more alien like. He heals super fast, is never sick etc. The boy is then found by some organization, but in fear he runs away before they can catch him. He flees to south america (i think) and finds love there. He stay for a long time until they find him once again. They kill his loved one but then he manages to fight off and escape once again. At the end he cuts open his wrist and he reveals that it was either hollow inside or green blood...?

I know this is a broad summary but please I would love to read this book again if anyone has any kind of idea of this book please let me know!!

Being by Kevin Brooks?

Jimmy Coates: Assassin? by Joe Craig ?

Yes that it, being by Kevin Brooks thank you so much :)

thanks