Ξεχάστηκα στο καφέ μιλώντας με μια συμφοιτήτριά μου και έφυγα πολύ αργά.

In this sentence, Ξεχάστηκα means something like I got carried away, I lost track of time, or I got so absorbed that I forgot about everything else.

So yes, the idea is related to forgetting oneself, but in natural English it usually means:

• I lost track of time
• I got caught up in the conversation
• I got distracted and stayed too long

It does not mean someone forgot me.

This is a very common learner question.

• ξέχασα = I forgot something
  
  • Ξέχασα τα κλειδιά μου = I forgot my keys
• ξεχάστηκα = I forgot myself / I lost track / I got carried away

So ξεχάστηκα is used when the speaker is the one who mentally drifted or became absorbed.

In this sentence, the idea is not that the speaker forgot a specific object or fact. The idea is that they were talking and became so absorbed that they stayed too long.

Because Greek usually does not need a subject pronoun when the verb ending already shows who the subject is.

Here:

• ξεχάστηκα = I got carried away
• έφυγα = I left

Both verb forms clearly show first person singular, so εγώ is unnecessary.

Greek can add εγώ for emphasis, contrast, or clarity, but most of the time it is left out.

στο is the contraction of σε + το.

So:

• σε το καφέ → στο καφέ

Here it means at/in the café.

Also, καφέ here means café / coffee shop, not the drink coffee.

A useful point: σε can mean in, at, or to, depending on context.
In this sentence, because of the meaning of ξεχάστηκα, it is understood as location:

• στο καφέ = at the café

Yes, το καφέ is very common in modern spoken Greek and means the café / coffee shop.

A few notes:

• το καφέ is colloquial and very common
• η καφετέρια is also very common and a bit more explicit
• both can refer to the kind of place where you sit and have coffee or drinks

So στο καφέ sounds natural.

μιλώντας is not a normal finite tense like μιλούσα or μίλησα. It is an adverbial participle, often called a gerund in learner materials.

It means:

• talking
• while talking
• as I was talking

So:

• μιλώντας με μια συμφοιτήτριά μου = while talking with a classmate of mine

This form is very useful in Greek for showing an action happening at the same time as another action.

Here με means with.

Greek commonly says:

• μιλάω με κάποιον = I talk with / to someone

So in this sentence, the focus is on being in conversation with someone.

You may also see μιλάω σε κάποιον, which can mean speak to someone, but μιλάω με κάποιον is extremely common for ordinary conversation.

This is a very important Greek structure.

In Greek, you can say:

• ένας φίλος μου = a friend of mine
• μια συμφοιτήτριά μου = a female classmate of mine

So μια + noun + μου is a normal pattern meaning:

• a ... of mine
• one of my ...

It does not sound ungrammatical in Greek, even though English cannot say a my classmate.

Also, because the noun is feminine, συμφοιτήτριά means female classmate.
A masculine version would be:

• ένας συμφοιτητής μου = a male classmate of mine

Because μου is an enclitic, a very short unstressed word that leans on the word before it.

When certain Greek words are followed by an enclitic like μου, σου, του, etc., Greek may add an extra written accent to show the correct pronunciation.

So:

• συμφοιτήτρια
• συμφοιτήτριά μου

That extra accent does not change the basic meaning of the noun. It is mainly about stress and pronunciation.

έφυγα means I left, I went away, or I headed off.

So:

• έφυγα πολύ αργά = I left very late

This is about the time of departure, not arrival.

Compare:

• έφυγα αργά = I left late
• ήρθα αργά = I arrived late

So the sentence is saying that because the speaker got absorbed in conversation, they did not leave until very late.

The sentence combines:

• two main past events: Ξεχάστηκα and έφυγα
• one simultaneous background action: μιλώντας

The time flow is basically:

1. the speaker was talking
2. while talking, they got carried away / lost track of time
3. as a result, they left very late

So μιλώντας provides the background circumstance, and the two aorist verbs give the main events.

Yes, it sounds natural and conversational.

The tone is everyday and informal-to-neutral. It feels like something someone would say when explaining why they were late getting home or why they stayed out longer than planned.

A key nuance is that Ξεχάστηκα makes the sentence sound very natural and idiomatic. It gives the sense that the speaker did not deliberately stay late; they just got caught up in the moment.