I've been working on diagramming this sentence: "It wasn't a safe place because the sound of the river masked any other but he thought it would cheer the boy up." The first entire half of the sentence, I think I got that down pretty well, but when it starts "he thought it would cheer the boy up" is when I start having trouble. I feel like there are just too many words! I don't know what to do with "it" coming between "thought would cheer". The splitting of the phrase "cheer up" isn't too big of a deal, I just smushed those back together. But what about the rest?
I attached what I ended up doing, which was putting it on a pedestal in the DO position as a participle but I have no idea if that is even remotely right.
This is good work. You seem to understand the syntax of the sentence. Just two things. It is conventional that coordinating conjunctions join clauses by the simple predicates, not their simple subjects. Also, the "because" clause should not be the one that the coordinating conjunction joins, but rather the independent (or main) clause.