O Pedro e a irmã abraçam-se depois do exame, mas não se beijam porque ele está doente.

In European Portuguese, it is very common to use the definite article before a person’s name in everyday language.

So:

• o Pedro = Pedro
• a Maria = Maria

This does not usually need to be translated into English. English says simply Pedro, but Portuguese often says o Pedro.

It is especially natural in Portugal. In more formal writing, the article may sometimes be left out, but in normal speech it is very common.

Portuguese often uses the definite article with family words when the relationship is clear from context.

So o Pedro e a irmã is understood as Pedro and his sister.

English usually needs a possessive word like his, but Portuguese does not always need it if the meaning is obvious.

If you wanted to make it more explicit, you could say:

• o Pedro e a sua irmã
• o Pedro e a irmã dele

In this sentence, a irmã is naturally understood as Pedro’s sister.

Here se shows a reciprocal action: the two people do the action to each other.

So:

• abraçam-se = they hug each other
• beijam-se = they kiss each other

This is different from a truly reflexive meaning like he washes himself. In this sentence, the meaning is reciprocal, not reflexive.

Because the subject is two people, se is best understood as each other.

This is a very important point in European Portuguese.

In a simple affirmative clause, the pronoun often comes after the verb:

• abraçam-se

But certain words, especially não, pull the pronoun before the verb:

• não se beijam

So the change happens because of não.

A simple way to remember it:

• affirmative main clause: often verb + pronoun
• negative clause: often pronoun + verb

That is why the sentence has:

• abraçam-se
• não se beijam

Both are in the present indicative, third person plural.

Why plural? Because the subject is two people:

• O Pedro e a irmã

So:

• abraçam = they hug
• beijam = they kiss

The endings -am are a common sign of third person plural in many verbs.

Because only ele is sick, not both people.

Compare:

• ele está doente = he is ill
• eles estão doentes = they are ill

In the sentence, the final part is:

• porque ele está doente

So the verb is singular because the subject is singular: ele.

Because ele is masculine singular, so it refers to a male person.

In the sentence, the two possible people are:

• Pedro = masculine
• a irmã = feminine

So ele can only refer to Pedro.

If the sister were the one who was ill, the sentence would say:

• porque ela está doente

Because depois normally takes de before a noun:

• depois de
  • noun

Then de + o contracts to do:

• depois de o exame → depois do exame

So:

• depois do exame = after the exam

This contraction is very common in Portuguese:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

Yes, that is possible in Portuguese, because Portuguese often drops subject pronouns when the meaning is clear from the verb or context.

So this would also be possible:

• ..., mas não se beijam porque está doente.

However, in this sentence, ele helps make the meaning very clear: it is he, not both of them, who is ill.

So the version with ele is especially useful for clarity.

Here porque means because, so this is the correct spelling.

In Portuguese, these forms are different:

• porque = because
• por que = why / for which reason, in some contexts
• porquê = the reason, as a noun
• por quê = used in some special sentence-final situations

In your sentence, it gives the reason:

• não se beijam porque ele está doente
• they do not kiss because he is ill

So porque is exactly right.

Yes. That would be perfectly correct and a bit more explicit.

Compare:

• O Pedro e a irmã abraçam-se...
• O Pedro e a sua irmã abraçam-se...

The original version sounds natural because Portuguese often leaves the possessive unstated when the relationship is obvious from context. But adding sua is also possible if you want to make the relationship clearer.