Since the show starts, Lucas is secretly in love with Peyton. He has simply a crush on her, about which only his best friend haley knows. He watches her via her punkanddisorderly webcam, they have a lot in common, even though Peyton is popular just like her best friend Brooke and dating most popular basketball player Nathan she feels lonely just the way Lucas is. They both are interested in the same music and stuff. Lucas is fascinated with Peyton. When he wants something more, she's afraid on engagement, of a serious relationship, because all she had with Nathan was just sex. For all this time also Brooke is very interested into Lucas, because Peyton is not honest with her about having feelings for Lucas, Brooke gets him first. Lucas thinks he has no chances with Peyton, he starts dating Brooke and notices she also amazing. So this is how its starts. Then watch entire show;)
Btw I'm Leyton fan but I love Brooke and there is a lot of epic Brucas scenes.