Should I get married in the US or Mexico?

It doesn't matter. However, once he leaves, he stays until the waiver is approved. The best play is to marry in the U.S., apply for naturalization 90 days prior to the 5 years of residency, then to file the family petition.

If your boyfriend is in the US and is not grandfathered by 245i, I'm assuming that he is in the US unlawfully. Even if you become a US citizen, you will not be able to help him legalize his status within the US. He would have to go back to his home country and consular process there but by departing the US, he will trigger an automatic 10 year bar to reentry, which can only be waived by a showing of extreme hardship to a US citizen spouse, which is fairly difficult to do in most cases.

It does not matter where you marry. When you are a US citizen you can process the case regardless of place of marriage.

Your situation requires a complete and thorough of all relevant issues before a decision as to where your marriage should take place can be made if you care about what to do serves the best interest of your boyfriend.

It does not matter where you get married as the USCIS recognizes the marriage in Mexico.

If your boyfriend is in the US now, it is probably better to get married in the US. If he is in Mexico, you can petition for him to enter the US as a fiance if he has no history of unlawful presence in the US. Otherwise, you will need to marry him in Mexico, but it could be years before he can enter the US.

It shall not matter where you get married. However, to give you suggestions, I would need further information. Your question does not state where your boyfriend currently resides. If he is in Mexico and cannot obtain a visa to travel to the US, then you may have to marry in Mexico to petition him or you may want to wait to become a citizen and then petition him as a fianc?. If he is in the United States, I would need to know how he entered the US. If he entered through the border he cannot adjust status (get residency) unless he leaves the US and goes through consular processing and present various waivers (not an easy case) depending on his situation. If he is in the US and entered with visa, even though the visa expired, then you should wait until you become a citizen to petition him and of course, you would get marry in the US. So, the answer depends on the facts of your specific case.

It depends on where your boyfriend is now and what, if any , US status he has. If he is in Mexico and is not barred due to other reasons(illegal presence, criminal convicitions, etc.), then bring him to US on a fiancee visa if possible. I would need more information, to discuss further.