Hello, this is attorney JoAnn Barten. It may be possible to help him become a permanent resident. First, it must be determined whether your fiance receive voluntary departure or if he signed an agreement for self-deportation and whether he has left the U.S. since his entry in 2005. Once these are determined and if he meets those requirements then your case would need to be a marriage case, not a fiance case. With this type of marriage case the U.S. government would require him to process through the U.S. consulate in Cuidad Juarez. It will require a waiver forgiving him for his unlawful presence in the U.S. Your fiance may have other legal options or possibly other violations which he may not be aware, so his case should be thoroughly reviewed by a competent immigration attorney before taking any steps.
I read the above answer, and agree.
However, in the event that your fiance was deported to Mexico, and returned illegally, he incurred the "permanent bar", meaning that he would have to remain outside the U.S. for ten years before he could even apply for a green card. He would always need a hardship waiver from the USCIS to return to the U.S.