If your boyfriend entered the US unlawfully AND noone had ever filed a petition on his behalf prior to April 30, 2001, you are correct in that he would be subject to the 10 year bar to reentry if he were to depart the US and, under the current immigration laws, he is not eligible to adjust status to permanent residence within the US even if you get married. (again, unless he has a petition that was filed on his behalf prior to April 30, 2001 which would grandfather him under Sec. 245i.The only way to waive the bar to reentry is to prove that there would be an extreme hardship to a US citizen spouse and children if he were to have to remain in Mexico.  For that, you would need to compile a vast amount of information and documentation from yourself, family members, doctors, etc. and see if you have a case.  Only then would I suggest going back to Mexico to try to do the waiver.  Again, this is only available to those who can prove hardship to a US citizen SPOUSE, so you would need to get married first and not just be engaged.You should discuss your specific situation and whether you have enough to warrant a waiver of the bar, with an immigration attorney.  Good luck.