I'm 18 years old and my parents want to move back to Mexico but I don't want to. I feel like they are going to make me move because they wouldn't want me to stay here by myself. I also have a boyfriend. We been dating for almost 3 years and I love him very much but my parents don't like him at all. We have talked about moving in together but I'm scared to say something to my parents. What should I do, stay here and live my life with my boyfriend, or listen to my parents and move with them to Mexico?

You are an adult, aren't you? Make a decision and follow through on it. Depend on your boyfriend. Depend on your parents. Or depend on YOURSELF.

What's the best option, and why?

Personally... your parents are probibly better judges of character than you are at 18. Make a mistake now and it will probibly follow you the rest of your life. And as an adult... its on you, you can't blame it on anyone else.

I wouldn't even begin to try to give advice unless you wrote at least 50 lines about yourself, your parents, your boyfriend, and your educational situations.
It's July and you are 18 - does that mean you have graduated from high school, I hope? As has he? Have you ever had a job? Do you know what apartments cost, even with 2 (low) incomes, never mind food and transportation? What is in Mexico that your parents miss? I'm afraid that you will be totally shocked out on your own, both of you.

You're considered an adult at 18 but you're afraid to tell your parents you want to move in with your boyfriend. That suggest to me it's a bad move.
How old is your boyfriend? Does he have a job, do you have one? Moving in with someone at 18 is more than a notion.

You are an adult. Like you said "you love your boyfriend so much", well, does he love you the same ? Will he be ready to take your responsibility ? And as you said your parents just don't like him at all, try to know the reason WHY they dislike him!
Is he not worthy for you ? Ask these questions to yourself, and know whether you get positive answers or not ! And if you get positive answer then just be brave and tell your parents about him I'm sure if the guy is nice and if you'll explain them why you want to stay with him ! They will definitely understand you. God bless for your future :)

At 18 your parents can not make you do anything, you need to decide and make your own plans