Learn Hardcore Portuguese (Portugal): Quando o casal discute por coisas pequenas, às vezes é só ciúmes. - When a couple argues about small things, sometimes it's just jealousy.

Using o casal discutem is considered incorrect in standard grammar, though you might hear plural agreement in very informal speech when people think more about “two people” than about the grammatical form. For learners, always use the singular verb with casal.

What does por mean in discute por coisas pequenas? Could I use sobre or nothing instead?

Here por indicates the reason / cause of the argument: they argue over / because of small things.

discutir por coisas pequenas = to argue over small things
discutir sobre coisas pequenas = to discuss/talk about small things (more neutral, like “talk about”)

Without any preposition:

discutir coisas pequenas is possible, but then it usually means “to discuss small things” in a more neutral, intellectual way, not “to argue because of them”.

So, for “argue over small things”, por is the most natural choice.

Is there a difference between por coisas pequenas and por pequenas coisas?

Both are correct and mean essentially the same, but the feel is slightly different:

por coisas pequenas – very common, neutral: “because of small things”
por pequenas coisas – also natural; the adjective is before the noun, which can add a bit of emphasis or “evaluative” tone: “because of such little things”

In this sentence, either order would sound fine:

Quando o casal discute por coisas pequenas…
Quando o casal discute por pequenas coisas…

Why is it às vezes with an accent, not as vezes?

Às vezes (with a grave accent) is a fixed expression meaning “sometimes”.

às = contraction of preposition a
- article as
vezes = “times”

Literally: “at the times” → “sometimes”.

As vezes (without accent) would normally be understood as “the times” (article + noun), not as “sometimes”, and in that meaning it usually appears inside a larger phrase:

Lembro-me de as vezes em que viajámos juntos. – I remember the times when we travelled together.

For “sometimes”, always write às vezes.

Why is ciúmes in the plural, but in English we say “jealousy” (singular)?

In Portuguese, ciúme / ciúmes behaves a bit differently from English jealousy:

The most common everyday form is ciúmes (plural form), especially in expressions like:
- ter ciúmes de alguém – to be jealous of someone
- é só ciúmes – it’s just jealousy

Even though ciúmes looks plural, here it works like a mass/uncountable noun, very similar to jealousy in English. You are not counting individual “jealousies”.

There is also ciúme (singular), which tends to feel a bit more formal or abstract:

O ciúme destruiu o relacionamento. – Jealousy destroyed the relationship.

In conversation, ciúmes is more typical in this kind of sentence.

Why is it é só ciúmes and not são só ciúmes?

The verb ser agrees with the subject, not with the complement.
Here, the subject is understood as a situation (the argument, the tension), and ciúmes is just describing what that situation is.

So you can think of it as:

[A situação] é só ciúmes. – [The situation] is just jealousy.

That invisible subject is singular, so the verb is singular: é.
Using são só ciúmes would sound wrong in standard Portuguese.

Why is there no article in é só ciúmes (not é só um ciúme or é só o ciúme)?

Because ciúmes here is being used like an uncountable or abstract noun, referring to jealousy in general:

é só ciúmes – it’s just jealousy (in general, non-specific)

If you add an article, you change the meaning:

é só um ciúme – sounds strange; “a jealousy” (counting an instance) is not natural.
é só o ciúme – could work in a very specific context (e.g., talking about “this particular jealousy that he feels”), but it’s much less common.

So in everyday speech, for the general idea, you normally omit the article: é só ciúmes.

Can I say só é ciúmes instead of é só ciúmes?

You can say só é ciúmes, but the emphasis changes and it sounds less natural in this specific sentence.

é só ciúmes – neutral, idiomatic: “it’s just jealousy”.
só é ciúmes – tends to stress só more, like “it’s only jealousy (and nothing else)”. It can sound a bit marked or awkward without more context.

In this kind of general statement about relationships, é só ciúmes is the strongly preferred word order.

Could I move às vezes to the beginning or the end of the sentence?

Yes. Portuguese is flexible with the position of às vezes. All of these are possible:

Às vezes, quando o casal discute por coisas pequenas, é só ciúmes.
Quando o casal discute por coisas pequenas, às vezes é só ciúmes. (original)
Quando o casal discute por coisas pequenas, é só ciúmes às vezes.

Differences:

At the beginning: slightly more emphasis on “sometimes”.
In the middle after the comma (original): very natural, common placement.
At the end: still correct, but can sound a bit looser or more conversational.

All are fine; the original word order is the most neutral.

Could I use se instead of quando here? What’s the difference?

Both are possible, but they don’t mean exactly the same:

Quando o casal discute por coisas pequenas, às vezes é só ciúmes.
= “When(ever) the couple argues over small things, sometimes it’s just jealousy.”
Quando suggests that this happens at times when such arguments occur.
Se o casal discute por coisas pequenas, às vezes é só ciúmes.
= “If the couple argues over small things, sometimes it’s just jealousy.”
Se is more hypothetical/conditional: if that situation happens.

In everyday speech, quando is more natural here because we’re talking about a recurring, real-life pattern, not a hypothetical condition.

Would Brazilians say this sentence in the same way?

They would understand it perfectly, but some word choices might change in Brazilian Portuguese:

Very natural Brazilian version:

Quando o casal briga por coisas pequenas, às vezes é só ciúme.

Main differences:

briga (from brigar) is more common than discute (from discutir) for “argue/fight” in Brazilian everyday speech.
ciúme (singular) is a bit more common in Brazil in this position, though ciúmes is also used.
The rest (quando, por coisas pequenas, às vezes) works in both varieties.