You have only known this young man online for a few months and were meeting him for the first time. I suspect your parents were trying to protect you from moving too fast into a sexual relationship with someone you barely know. I agree. It’s easy for your boyfriend to urge you to “cut the cord,” but he’s not the one risking their support and respect. You are. Although you are 21, you are still living in your parents’ home and they are supporting you. For that reason, both you and your boyfriend needed to respect their rule. The fact that the two of you “sneaked” only proved to them that you are immature and that the boyfriend can’t be trusted.
My advice to you is to slow down. Your parents are right that you know very little about this guy and his family. You don’t need to rush into a sexual relationship with him or a long visit with his parents. You have plenty of time to see how this relationship unfolds and if the interest turns to real love. Doing well in school is your road to eventually being an independent adult. If your guy loves you, he will take the time to really get to know you. He will honor your family and support you in your schooling — not just pursue his own goals.
I wish you well.