Ok, so first thing I noticed there's a lot of unnecessary dialogue which could be removed and the story is still understandable. You could skip kathen's and his mom's convo and start with an establishing shot of the living room. He hears the t.v. , listens, and reacts to it. Cutting the unnecessary convo saves you time from having to draw it's panels. And you don't have to illustrate the mom telling kathen his friend is outside, he could just look at the window and see the friend there.
When writing the script ask yourself; will the story, mood, progression, and pace be just as good if I remove this?
And about plot...a good method is to figure out your ending and theme. That'll be your guide on how to build the plot's progression.
I'll make something up from your story as an example. Let's say the theme is about naivety and how trusting others easily is a harmful to yourself. So from that, the ending could be his friend being a murderous stalker and almost ends up killing kathen but somehow he survived and the friend goes to prison. Based on the ending and the theme, you could first establish kathen blindly trusting his friend and as the plot progresses, he notices stalkerish signs about the friend. BUT he ignores every sign because he believes everyone is kind (which shows the theme) until we get to the ending.
I'm not saying that should be the plot, but the structure could go like that. Use the ending and the theme as guides. Ugh, I say this because this is the same mistake I did and I only found out about this 5 chapters in my comic. Good luck writing!