Question

Which comma rule does this student need to apply to this passage?

I really thought she loved me but I discovered her grave betrayal one afternoon. It was easy to figure out because she accidentally sent a text to me that was meant for him. I was confused by the text because it said, "Don't tell Mike." I felt insulted that she thought she could get away with this infidelity. At first I felt very angry but then I felt so hopeless and depressed

Answer 1

So, in the example, there are commas missing in many places. The most obvious would be in the case of a compound sentence. Whenever two independent clauses are in the same sentence, they must be separated by a comma and a conjunction (unless you're using a semicolon or you're going for a particular style, but that's neither here nor there).
I'll assume you know how to identify compound sentences.
The next case you'd use a comma for is complex sentences. This is a type of sentence made up of a dependent clause (only a subject with no verb, for instance, or maybe only an object), followed by an independent clause (made up of at least a subject and a verb). With this information, I think you should be able to identify where commas are needed in the passage above. I'm not sure what 'comma rules' the question might be asking about, though.