Я злюсь не потому, что ты опоздал, а потому, что ничего не сказал.

Я злюсь means I’m angry / I’m getting angry / I’m mad as a state expressed with a verb.

• злиться = to be angry, to get angry
• злой = angry, mean, evil, злой is an adjective

So:

• Я злюсь = I’m angry / I’m upset
• Я злой = I’m angry / I’m an angry person

In this sentence, Russian prefers the verb because it describes the speaker’s emotional reaction to the situation.

Because the verb is злиться, which is a reflexive verb.

Its infinitive is:

• злить = to anger someone
• злиться = to be angry / get angry

Examples:

• Это меня злит. = That makes me angry.
• Я злюсь. = I’m angry.

The -ся / -сь ending is very common in Russian and often marks a verb that describes a state or reaction involving the subject.

This is a very common Russian pattern meaning:

not because..., but because...

So the sentence literally works like this:

• Я злюсь не потому, что ты опоздал
  = I’m angry not because you were late
• а потому, что ничего не сказал
  = but because you didn’t say anything

It is used to correct the listener’s assumption and show the real reason.

A useful model to remember:

• не потому, что X, а потому, что Y
  = not because X, but because Y

Both ideas are useful.

Normally, потому что is the standard conjunction meaning because:

• Я ушёл, потому что устал.
  = I left because I was tired.

But in this sentence, Russian is using the contrast pattern:

• не потому, что..., а потому, что...

Here, потому is part of the correlative structure with не and а. So it feels a bit more like:

• not for the reason that..., but for the reason that...

That is why the sentence is built this way instead of simply using one plain потому что clause.

Because что introduces subordinate clauses.

In this sentence:

• не потому, что ты опоздал
• а потому, что ничего не сказал

each что begins a clause with its own subject and verb:

• ты опоздал
• (ты) ничего не сказал

Russian punctuation normally separates these subordinate clauses with commas.

So the commas are not optional here.

Because Russian past tense agrees with gender in the singular.

• опоздал = masculine
• опоздала = feminine
• опоздало = neuter
• опоздали = plural

So if the speaker is talking to a man:

• ты опоздал

If talking to a woman:

• ты опоздала

The same applies to сказал / сказала later in the sentence.

So to a woman, the full sentence would be:

• Я злюсь не потому, что ты опоздала, а потому, что ничего не сказала.

Yes, and that is normal in Russian.

Russian commonly uses negative concord, which means multiple negative words appear together in one negative sentence.

So:

• ничего не сказал = literally said nothing not
• natural English meaning: didn’t say anything / said nothing

More examples:

• Я ничего не знаю. = I don’t know anything.
• Он никого не видел. = He didn’t see anyone.
• Мы никогда не спорим. = We never argue.

In English, standard double negatives are usually wrong, but in Russian they are often required.

Because ничего is the correct negative pronoun meaning nothing / anything in negative sentences.

Compare:

• что-то сказал = said something
• ничего не сказал = said nothing / didn’t say anything

Russian does not say не что сказал for this meaning.

A useful pair:

• кто-то = someone

• никто не = no one / nobody ... not

• что-то = something
• ничего не = nothing / anything ... not

This is about aspect.

• сказать = perfective, to say something as a completed act
• говорить = imperfective, to speak, to say, to be saying, to talk

In this sentence, the speaker is upset because the other person failed to say something when they should have. That is a missing completed action, so не сказал is the natural choice.

• ничего не сказал = didn’t say anything
• ничего не говорил can also exist, but it sounds more like wasn’t saying anything / didn’t speak about it / didn’t mention it over a period of time

Here the point is a single expected act of informing the speaker, so не сказал fits best.

Russian often omits pronouns when they are already clear from context.

The first clause has:

• ты опоздал

So in the second clause, the listener is obviously the same person, and Russian can simply say:

• ничего не сказал

The omitted subject is still understood as ты.

You could say:

• ...а потому, что ты ничего не сказал

but it is less natural unless you want extra emphasis on you.

In this pattern, а is the normal conjunction.

• не потому, что..., а потому, что...

Here а introduces a contrast/correction:

• not X,
• but rather Y

This is slightly different from plain но, which often just means but in a more general sense.

With this exact paired structure, а is what Russian normally uses.

Yes, but the original order is the most natural and clear.

Standard version:

• Я злюсь не потому, что ты опоздал, а потому, что ничего не сказал.

You could sometimes reorder parts for emphasis, but that may sound more literary, emotional, or marked.

The given word order is good because it clearly presents:

1. the wrong assumption
2. the real reason

That is exactly how this contrast structure is usually used.

Yes, that is a very natural English interpretation.

Russian uses a because structure:

• не потому, что..., а потому, что...

But the idea in natural English is often:

• I’m not angry that you were late; I’m angry that you didn’t say anything.
• It’s not the lateness that bothers me, it’s the fact that you didn’t say anything.

So even though the Russian wording uses because, the real communicative meaning is often about the true cause of the speaker’s anger.