Μερικές φορές ζηλεύω τη φίλη μου γιατί μιλάει ελληνικά πιο γρήγορα από εμένα.

Because η φίλη μου is the subject form (nominative), and τη φίλη μου is the object form (accusative).

• η φίλη = the (female) friend (subject)
• τη φίλη = the (female) friend (object)

In this sentence, τη φίλη μου is what you are jealous of, so it’s the object of the verb ζηλεύω:

• ζηλεύω τη φίλη μου = I am jealous of my friend / I envy my friend.

The μου is the possessive pronoun “my”, and in Greek it normally comes after the noun:
η φίλη μου, το βιβλίο μου, ο αδελφός μου.

Both την φίλη and τη φίλη can be correct; the difference is about the final -ν.

The feminine article την often drops the final -ν in writing and becomes τη, especially:

• before consonants like φ, θ, χ, σ, ζ, ξ, ψ, ρ, λ, μ, ν
• in informal/modern writing

So:

• την αγαπώ (before a vowel → we usually keep the ν)
• τη φίλη μου (before φ, many people drop the ν and write τη)

You will see both in real Greek. For learners, it’s always safe to keep the -ν: την φίλη μου. Many native speakers, however, write τη φίλη μου in informal contexts.

In Greek, ζηλεύω works like a normal transitive verb: it takes a direct object in the accusative, with no preposition.

• ζηλεύω τη φίλη μου = I am jealous of my friend / I envy my friend.
• ζηλεύω τον αδελφό μου = I am jealous of my brother.

So you do not say ζηλεύω από τη φίλη μου or ζηλεύω για τη φίλη μου here. Those would be wrong in this meaning.

Also note the meaning:

• ζηλεύω κάποιον = I envy someone / I am jealous of someone (because of something they have or can do).
• είμαι ζηλιάρης / ζηλιάρα = I am a jealous person (more about character).

Both μιλάει and μιλά are correct 3rd person singular forms of μιλάω / μιλώ (to speak).

• μιλάει – more common in informal spoken Greek; feels a bit more “full”.
• μιλά – a bit shorter / more formal / more written, but also used in speech.

They are completely interchangeable here:

• … γιατί μιλάει ελληνικά …
• … γιατί μιλά ελληνικά …

They both mean “because she speaks Greek …”.

In Modern Greek, names of languages are usually treated as neuter plural nouns:

• τα ελληνικά – the Greek language
• τα αγγλικά – English
• τα γαλλικά – French

But in many everyday sentences, the article is dropped, and the bare form is used:

• μιλάει ελληνικά = she speaks Greek
• μαθαίνω ελληνικά = I’m learning Greek
• ξέρω ελληνικά = I know Greek

You can say η ελληνική γλώσσα (literally the Greek language), but that sounds much more formal or textbook-like in everyday speech.

After verbs like:

• μιλάω (speak),
• μαθαίνω (learn),
• ξέρω (know),
• καταλαβαίνω (understand),

Greek usually drops the article with language names:

• μιλάω ελληνικά
• μαθαίνω αγγλικά
• ξέρω λίγα γαλλικά

You normally do not say μιλάει τα ελληνικά in this sense; it sounds odd or at least non‑idiomatic.

You use τα ελληνικά more when you talk about the language as a subject or object of study:

• Τα ελληνικά είναι δύσκολα. – Greek (as a language) is difficult.
• Κάνω μάθημα στα ελληνικά. – I have a lesson in Greek.

Greek has two ways to form the comparative of many adverbs and adjectives:

1. πιο + adverb/adjective (very common in modern speech)
   • πιο γρήγορα – faster / more quickly
2. A single comparative form in -ότερα (adverb) or -τερος / -τερη / -τερο (adjective)
   • γρηγορότερα – faster / more quickly (adverb)
   • γρηγορότερος – faster (adjective, masculine)

In everyday Modern Greek, πιο + base form is more frequent, especially in speech:

• Μιλάει πιο γρήγορα από εμένα.

You could say μιλάει γρηγορότερα από εμένα, and it’s grammatically correct, but it sounds a bit more formal or less common in casual speech.

Because here “faster” refers to how she speaks (the manner of speaking), so you need an adverb, not an adjective.

• γρήγορα – adverb = quickly, fast
• γρήγορη – adjective, feminine = fast (female thing/person)
• γρήγορος – adjective, masculine

So:

• Μιλάει γρήγορα. – She speaks quickly. (adverb)
• Είναι γρήγορη. – She is fast. (adjective, describing her)

In the sentence, πιο γρήγορα = more quickly, faster → correct adverbial form.

Yes, από usually means “from”, but after a comparative it also means “than”.

Structure:

• πιο + adjective/adverb + από + noun/pronoun

Examples:

• Είναι πιο ψηλή από εμένα. – She is taller than me.
• Μιλάει πιο γρήγορα από εμένα. – She speaks faster than me.
• Τρέχει πιο γρήγορα από τον αδελφό της. – She runs faster than her brother.

So in this context, από is best translated as “than”, not “from”.

Both από εμένα and από μένα mean “than me / from me” here. The difference is very small and mostly about emphasis / style:

• εμένα – the full, strong form of the pronoun (more emphasis)
• μένα – a slightly weaker / shorter form (very common in speech)

You can think of:

• από εμένα ≈ than me (with a bit of emphasis)
• από μένα ≈ than me (more neutral)

In everyday speech, από μένα is extremely common. In your sentence, both are fine.

Yes. Literally:

• μερικές = some (feminine plural)
• φορές = times

So μερικές φορές = some times, and idiomatically it means “sometimes”, just like in English.

It’s a very common expression:

• Μερικές φορές αργώ στη δουλειά. – Sometimes I’m late to work.
• Μερικές φορές ζηλεύω τη φίλη μου… – Sometimes I’m jealous of my friend…

You can also hear:

• καμιά φορά – also “sometimes” (often slightly more casual/colloquial)
• πότε πότε – “from time to time”

But μερικές φορές is a very standard, neutral way to say “sometimes.”

Yes, Greek word order is fairly flexible, and your version is correct.

Original:

• Μερικές φορές ζηλεύω τη φίλη μου γιατί μιλάει ελληνικά πιο γρήγορα από εμένα.

Variant:

• Μερικές φορές ζηλεύω γιατί η φίλη μου μιλάει ελληνικά πιο γρήγορα από εμένα.

The difference is only in focus:

• Original: highlights whom you’re jealous of (τη φίλη μου).
• Variant: first states that you get jealous, then explains why (because your friend speaks faster).

Both are natural; the original is slightly more compact and keeps τη φίλη μου close to ζηλεύω, which is very typical.