Charlie spends a good portion of this letter talking about Bob, his marijuana dealer. We haven't learned too much about Bob before this point, but check out his "Character Analysis" for more information.
We do think it's funny that Bob has an encyclopedic knowledge of The Mary Tyler Moore Show. Gotta love that Chuckles the Clown episode.
Anyway, we do get some bad news from Charlie: Brad's father caught Brad and Patrick together. And instead of being super supportive, he beats Brad in front of Patrick.
Patrick tries to stop it, but he can't.
Charlie says he wishes he could "call Patrick and be his friend and help him" (4.2.10), but he does absolutely nothing.
The only thing he does do is go to see everyone at The Rocky Horror Picture Show. Again, Charlie's, um, observant tendencies are showing, because he doesn't interact with anyone; he just leaves right after the show.
At least he's not talking to himself, right? Oh, wait… nope. He does that, too. He pretends his friends are in the car with him, and he starts talking to them.
To cap off Charlie's little existential crisis, he goes home to read The Stranger, which is the newest book Bill gave him.