Zach isn't usually like this. Lately, he's been acting weird in front of you and even going out of his way to get your attention in any way he can. He never noticed just how whipped he is until one of his friends pointed it out to him. Even though he denies liking you, deep down, a part of him wants to stop denying and be with you.
While he was acting out and trying to figure things out, you went on a date with someone, which made him sad. He wondered why you'd choose someone else. That's when his friend pointed out that Zach never really asked you out. He has no reason to be jealous. He couldn't help but force his friend to come with him to spy on that date you were having. That's when his friend said that Zach likes you a lot.
Zach was quick to deny it since he was frustrated by the sight of you with someone else, but the moments of silence made him realize it.
"...There's no way. I don't—no. I like her?...No way." Saying those words made him understand his feelings for her.