Learn Hardcore Greek: Ο φίλος μου χώρισε με τη φίλη του γιατί δεν συμφωνούσαν ποτέ. - My friend male broke up with his girlfriend because they never agreed.

The little words μου, σου, του, της, μας, σας, τους are weak possessive pronouns and normally come after the noun they belong to, not before it.

Putting μου before the noun (μου φίλος) is not standard; it would sound wrong in normal Greek.

What is the role of Ο in Ο φίλος μου? Why is there a definite article?

Ο is the masculine singular definite article in the nominative case, like the in English.

Greek uses the definite article much more than English, especially:

with people: ο φίλος μου, η αδερφή μου, ο Γιάννης
with abstract nouns and general concepts

Here Ο φίλος μου means specifically my friend (a particular, known person). You normally must use the article in such a case; Φίλος μου χώρισε… sounds incomplete or poetic/marked.

Why is it τη φίλη του and not την φίλη του in writing?

The feminine accusative singular article is historically την, but in modern usage the ν (nu) at the end often drops in front of many consonants:

Before κ, π, τ, μπ, ντ, γκ, ξ, ψ and vowels, you usually keep the ν:
- την κόρη, την ταινία, την ψυχή
Before other consonants (like φ in φίλη) you can drop it:
- τη φίλη (instead of την φίλη)

So:

τη φίλη του is the common modern spelling.
In careful/formal writing you may also see την φίλη του, which is not wrong.

In speech, many people still pronounce it close to [tin fíli] even when they write τη φίλη.

Why do we say χώρισε με τη φίλη του? Is με (with) necessary? Could we say just χώρισε τη φίλη του?

The verb χωρίζω has a couple of relevant uses:

intransitive + με + person = to break up (with someone)
- Ο φίλος μου χώρισε με τη φίλη του.
  → My friend broke up with his girlfriend.
transitive (χωρίζω κάποιον) can mean
- literally to separate someone (from something)
- or colloquially also to break up with someone:
- Ο φίλος μου χώρισε τη φίλη του.
  Literally: he separated his girlfriend.
  In everyday speech, many people use this to mean he dumped his girlfriend / broke up with her.

So:

χώρισε με τη φίλη του is very clear: broke up with his girlfriend.
χώρισε τη φίλη του is also heard with similar meaning, but without με it can sound a bit more like he dumped her (slightly more one-sided).

What tense is χώρισε and why not χώριζε?

χώρισε is aorist (simple past). It presents the breakup as a single, completed event:

Ο φίλος μου χώρισε με τη φίλη του
→ My friend broke up with his girlfriend (once, at some point).

χώριζε would be the imperfect (past continuous / repeated):

Ο φίλος μου χώριζε με τη φίλη του
→ He was breaking up with his girlfriend / kept breaking up with her (sounds odd here, as if they broke up repeatedly).

For a normal “they broke up once” situation, Greek uses the aorist: χώρισε.

Why is συμφωνούσαν in the plural? The sentence starts with Ο φίλος μου (singular).

The verb συμφωνούσαν has no expressed subject in that clause; the subject is understood from context.

From the first part we know there are two people involved:

Ο φίλος μου (my friend)
η φίλη του (his girlfriend)

So in γιατί δεν συμφωνούσαν ποτέ, the understood subject is they (my friend + his girlfriend), which is third person plural:

(Αυτοί) δεν συμφωνούσαν ποτέ.
→ They never agreed.

That’s why the verb is plural: συμφωνούσαν, not συμφωνούσε.

Why is συμφωνούσαν (imperfect) used instead of συμφώνησαν (aorist)?

The choice of tense shows type of action in the past:

συμφώνησαν (aorist): they agreed (once, at a particular moment).
συμφωνούσαν (imperfect): they didn’t use to agree, they never agreed, it was a repeated/habitual situation.

In γιατί δεν συμφωνούσαν ποτέ:

imperfect + ποτέ describes a long‑term pattern or habitual failure to agree.
This explains why they broke up: not one argument, but that they never got along / never agreed over time.

So the imperfect is the natural choice here.

Could we say γιατί ποτέ δεν συμφωνούσαν instead of γιατί δεν συμφωνούσαν ποτέ? Is there a difference?

Both are grammatical and mean essentially the same:

γιατί δεν συμφωνούσαν ποτέ
γιατί ποτέ δεν συμφωνούσαν

Differences:

Common, neutral order: δεν + verb + ποτέ
- This is the most usual in everyday speech.
ποτέ δεν + verb gives a slight emphasis on ποτέ (“never they agreed”), but it’s a subtle nuance.

In practice you can use either. The original word order is very natural.

Is γιατί here “why” or “because”? Could we use επειδή instead?

γιατί in Greek can mean both:

why (in questions)
because (in answers and statements)

In this sentence it clearly means because:

… γιατί δεν συμφωνούσαν ποτέ.
→ … because they never agreed.

You could also say:

Ο φίλος μου χώρισε με τη φίλη του επειδή δεν συμφωνούσαν ποτέ.

επειδή = “because” only (never “why”) and sounds just a bit more formal or explicit as a causal connector. Both are correct here; γιατί is extremely common in speech.

Does φίλος / φίλη always mean “boyfriend/girlfriend”? How do we know it’s romantic here?

Literally:

φίλος = (male) friend
φίλη = (female) friend

Whether it is romantic depends on context:

Ο φίλος μου could be:
- my male friend
- my boyfriend
η φίλη του could be:
- his female friend
- his girlfriend

Here, because of the verb χώρισε (με), which is typically used for romantic breakups, we understand τη φίλη του as his girlfriend.

If you want to be absolutely clear and explicitly romantic, you can also say:

το αγόρι μου = my boyfriend
η κοπέλα μου = my girlfriend

Why are μου and του both used for different genders but translated as “my” and “his”? Shouldn’t they change?

The weak possessive pronouns:

μου = my
σου = your (singular)
του = his / its
της = her / its
μας = our
σας = your (plural / polite)
τους = their

do not change form according to the gender of the noun they modify. They stay the same and only the article and noun show gender and case:

ο φίλος μου (masc.) = my (male) friend
η φίλη μου (fem.) = my (female) friend
το παιδί μου (neut.) = my child

In η φίλη του, του is masculine because it refers to him (the friend), not because of the gender of φίλη. The gender of the possessor is in the dictionary meaning:

του → belonging to him

Could we drop μου or του and just say Ο φίλος χώρισε με τη φίλη? Would that still work?

Grammatically you can say:

Ο φίλος χώρισε με τη φίλη.

But:

It sounds incomplete and unnatural in most contexts. Listeners expect some way to identify which friend and whose girlfriend.
Without μου and του, you lose:
- that it is my friend
- that she is his girlfriend

So in normal speech you would almost always keep the possessives:

Ο φίλος μου χώρισε με τη φίλη του.

Dropping them is only natural if the context already made these relationships completely clear just before, and even then it would sound a bit stylistic or literary.