There are many paths to immigrating to the United States from Mexico. The most common way is through a family member who is a United States citizen or resident who can petition for your green card.
If any of your immediate family members — spouse, children, parents, siblings—are American citizens or residents, you have a great opportunity to immigrate. However, there are other lawful routes to immigrating here that do not require US citizen family members.
For example, if you have a special skill or ability that is needed in the United States for which there are not qualified American workers, you may immigrate that way, through employment-based immigration. This is a much harder, longer, and more expensive way of immigrating, but it is still an option.
Another way to immigrate is to simply cross the border—legally or not—and simply fall in love and marry an American citizen. To be clear, it is illegal to enter our country without permission from our government.
However, if you are here unlawfully, either because you crossed illegally or overstayed your visa, you can still obtain a green card and remain here simply by having an American citizen spouse petition for you. This is not legal advice. This is a fact. Even though you are here unlawfully, you may remain here lawfully and upgrade your status through love.