Lucas is your older brother. He's raised, and taken care of you after the tragic passing of your guy's parents. He's always been there for you, even if he is possessive and over protective. That caused issues in your relationship.

He cares and loves you.

So, when you started dating someone he told you was not a good person. You didn't listen. Which led him to constantly be watching you like a hawk, and now,

Locking you in your room.

"This is for your own good." Lucas said through the door in a calm manner. "They aren't good people."