I am getting married to a non-U.S. citizen and need to know all the correct steps to take to take.

Your partner’s difficulty is that if he resided in the U. S. illegally for 7 years, he is subject to a 10 year bar for the illegal stay. He would require a waiver based upon extreme hardship to you if the waiver was not granted. My advice would be for you to be married in another country where gay marriage is legal and then for you to apply for him on form I-130 for an immigration visa. At interview, he would be denied and instructed that he could file the waiver application. Assuming that the waiver application is approved, he would enter the U. S. as a conditional permanent resident or permanent resident dependent upon the length of your marriage by the date of his entry.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.  

Because your partner was in the US without authorization for more than a year, he will be barred from returning for 10 years (7 more years, since he has been gone for 3 already).  A waiver is available for this bar.  He will have to resolve this before coming on any visa. http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=bb515f56ff55d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=db029c7755cb9010VgnVCM10000045f3d6a1RCRD