How can I help my boyfriend go through naturalization?

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated I strongly suggest that you boyfriend contact an experienced immigration attorney for a face-to-face consultation and give him/her all of the facts surrounding his situation. (S)he would then be in a better position to analyze his case and advise you of your options.

Need more details to analyze this matter.

If you and your boyfriend get married, as I think you indicated that you are planning to do, then you can apply for an immigrant relative petition for your boyfriend. However, if he is illegally present in the US, then he would most likely not eligible to apply for adjustment of status to permanent resident ("Greencard") in the U.S. (unless he had a petition filed on or before April 30, 2001, for him or for a relative, like his parent, and he was the beneficiary of such a petition). If he doesn't have a prior petition, then he would not be eligible for adjustment of status, and that means that he would have to do consular processing of his immigrant visa in his home country. That is, he would have to do his immigrant visa interview in his home country. However, doing consular processing would mean that he would be subject to a 10-year bar to reentry into the U.S. He may even face more serious bar if he has left and entered the U.S. illegally several times. I suggest that you and your boyfriend consult with an immigration attorney about his case, since his case is quite complex.

He would first need to get a green card. If he's married to a USA citizen, you could start the process by doing a visa petition for him.