I really want to know if it is the same as Shirk. I saw something like that in a comment of a post (link: Do actions (kissing, touching, etc) which could lead to zina (sex before marriage) count as a major sin?). This is the comment: "This does not mean that sins committed with intent are unforgivable - but IMHO it means that forgiveness is much harder to obtain for those... because "sinning with intent" means "actively defying Allah" which in itself is a major sin. – Yahia Aug 14 '13 at 14:41"
Is sinning with intent same as Shirk?
Absolutely not. Shirk means associating with Allah, not defying him, those two things are clearly different.
I can believe in Allah as the one true God, but disobey him in practicing Zina or drinking Wine because of my weak will. For such things there is something called punishments, which you get.
Small sins can be washed away by doing good, praying, etc..