how can i help my fiance get llegal in the US?

If he was deported and then returned to the U.S. illegally, he is subject to a "permanent bar" to obtaining his residency.  There is a waiver of the permanent bar after he has lived outside the U.S. for ten years.  He will not be able to get a green card for ten years or more. I suggest that you consult with an experienced immigration attorney before you tie the knot.   Good luck, Mark