Learn Hardcore Spanish (Spain): Él estaba celoso, pero decidió perdonar el error de su novia. - He was jealous, but he decided to forgive his girlfriend’s mistake.

To emphasize the subject: HE was jealous (not someone else).
To make things extra clear in context (for example, if several people were mentioned before).

So it’s optional, but not wrong.

Why is estaba (imperfect) used, but decidió (preterite) is used in the same sentence?

This is a classic contrast of Spanish past tenses:

estaba celoso (imperfect)
- Describes a background state, ongoing feeling, or situation.
- He was (felt) jealous over some period of time.
decidió perdonar (preterite)
- Describes a completed action at a specific point.
- He decided to forgive (one clear decision).

So the structure is:

Background: Él estaba celoso,
Completed action against that background: pero decidió perdonar…

Could you say Él era celoso instead of Él estaba celoso? What’s the difference?

Yes, but it changes the meaning:

Él estaba celoso
- Temporary emotion or state in that moment or situation.
- He was (feeling) jealous then.
Él era celoso
- Describes a more permanent trait of his character.
- He was (a) jealous person in general.

In this sentence, the idea is that he felt jealous in that specific situation, so estaba is more natural.

Why is it celoso and not celosa here?

Adjectives in Spanish agree with the gender and number of the noun or pronoun:

Él estaba celoso → él is masculine singular → celoso
Ella estaba celosa → ella is feminine singular → celosa
Ellos estaban celosos → masculine plural → celosos
Ellas estaban celosas → feminine plural → celosas

Here the subject is él, so we use celoso.

What’s the difference between celoso and envidioso?

They are related but not the same:

celoso = jealous
- Typically about a relationship or something you “possess”:
  - Está celoso de su novia. = He is jealous about his girlfriend.
  - Está celoso de su hermano (because of parents’ affection, etc.).
envidioso = envious
- About what others have (money, talent, success):
  - Está envidioso de su compañero porque gana más.
    = He is envious of his coworker because he earns more.

In this sentence, we’re talking about his girlfriend and her “error”, so celoso is the natural choice.

Why is it decidió perdonar and not decidió de perdonar or decidió a perdonar?

In Spanish, when decidir is followed by a verb, it goes directly with the infinitive without a preposition:

decidir + infinitive
- Decidió perdonar. = He decided to forgive.
- Decidimos salir. = We decided to go out.
- He decidido estudiar más. = I’ve decided to study more.

Using de or a before the infinitive here would be incorrect:

✗ decidió de perdonar
✗ decidió a perdonar

Why is it perdonar el error and not perdonar a su novia? Are both possible?

Both are possible but they focus on different things:

perdonar el error (de su novia)
- Direct object = the mistake.
- Focus: the specific action she did wrong.
- He decided to forgive his girlfriend’s mistake.
perdonar a su novia (por su error)
- Direct object = the person, marked with a:
  - perdonar a + person.
- Focus: forgiving her as a person.
- He decided to forgive his girlfriend (for her mistake).

So the grammar is:

perdonar + cosa → no a: perdonar el error
perdonar + a + persona → perdonar a su novia

Why do we say el error and not just perdonar error without the article?

In Spanish, you normally need a definite article (el, la, los, las) with singular countable nouns, much more often than in English.

English often drops “the” in general or abstract statements:

He decided to forgive the mistake / forgive mistakes.

Spanish usually keeps the article:

Decidió perdonar el error.
Perdonó la falta.

You would only drop the article in some fixed expressions or after certain verbs and prepositions, but here el error is the natural, standard form.

Why is it el error de su novia and not el error a su novia?

The preposition de here marks possession or relationship:

el error de su novia = his girlfriend’s mistake / the mistake of his girlfriend.

The preposition a is not used to show possession; it is used mainly:

For indirect objects: Le dio un regalo a su novia.
For direct objects that are people: Perdonó a su novia.

So:

el error de su novia = the mistake of his girlfriend.
perdonó a su novia = he forgave his girlfriend.

Does su mean “his” or “her” here? How do you know?

Su is ambiguous in Spanish; it can mean:

his
her
their
your (formal, singular or plural: usted / ustedes)

In this sentence:

el error de su novia
could be “his girlfriend’s mistake” or “her girlfriend’s mistake” depending on context.

If you want to make it crystal clear, you can use:

el error de su novia (context-dependent)
el error de su novia, de él = his girlfriend’s mistake
el error de su novia, de ella = her girlfriend’s mistake

But in real conversations, context almost always makes it obvious.

What exactly does novia mean in Spain? Is it just “girlfriend”?

In Spain, novia can mean:

Girlfriend (in a romantic relationship, not casual dating)
- Es mi novia. = She’s my girlfriend.
Fiancée (engaged to be married)
- Mi novia y yo nos casamos el año que viene.
Bride (on the wedding day)
- La novia llegó a la iglesia. = The bride arrived at the church.

The masculine form is novio (boyfriend / fiancé / groom).

If you want a more neutral word like “partner,” people also say pareja:

Es mi pareja. = He/She is my partner.

Could you replace pero with aunque here? What’s the difference?

You could say Aunque estaba celoso, decidió perdonar…, but the structure changes slightly:

pero = but
- Connects two clauses and introduces a contrast:
  - Estaba celoso, pero decidió perdonar…
    = He was jealous, but he decided to forgive…
aunque = although / even though
- Introduces the first clause as a concessive idea:
  - Aunque estaba celoso, decidió perdonar…
    = Although he was jealous, he decided to forgive…

Both express contrast; with pero you state A and then oppose it with B; with aunque you present A as a concession to B. Both are natural; they just organize the information differently.