Bukan hanya saya yang merasa cemas, melainkan juga teman perempuan saya.

It is a set pattern meaning not only ..., but also ....

So:

• bukan hanya saya = not only me / not only I
• melainkan juga teman perempuan saya = but also my female friend

This pattern links two parallel elements. In this sentence, the two parallel elements are:

• saya
• teman perempuan saya

Both of them are understood as the people who merasa cemas.

That is a very common learner question, because both bukan and tidak can appear in patterns that translate as not only.

Here, bukan hanya is a normal fixed expression. You should learn it as a chunk.

In general:

• tidak usually negates verbs and adjectives
• bukan usually negates nouns or identity/classification

But in real Indonesian, certain expressions become standard as set phrases, and bukan hanya is one of them.

You may also hear:

• tidak hanya ..., tetapi juga ...
• bukan hanya ..., tetapi juga ...

So the choice is partly grammatical and partly idiomatic.

Melainkan is a conjunction that often appears after a negative idea and means something like but rather, but instead, or in this structure, but also.

In this sentence, it is part of the pair:

• bukan hanya ..., melainkan juga ...

Compared with tetapi:

• tetapi is a general but
• melainkan often sounds a bit more corrective or contrastive
• melainkan can feel slightly more formal or written

A very common alternative would be:

• Tidak hanya saya yang merasa cemas, tetapi juga teman perempuan saya.

That has basically the same meaning.

Here, yang introduces a relative clause.

• saya yang merasa cemas literally means something like I, who feel anxious or the one who feels anxious is me

In more natural English, you would not usually translate it literally, but grammatically it helps connect saya to merasa cemas.

So the structure is roughly:

• bukan hanya [saya yang merasa cemas]
• melainkan juga [teman perempuan saya]

The yang shows that saya is the person doing or experiencing merasa cemas.

Because Indonesian often omits repeated information when it is already clear.

The full expanded version would be:

• Bukan hanya saya yang merasa cemas, melainkan juga teman perempuan saya yang merasa cemas.

But that sounds repetitive, so the second yang merasa cemas is dropped.

This is very common in Indonesian. Once the listener knows the second noun phrase belongs to the same description, repetition is unnecessary.

Both are natural, but they are slightly different in form.

• cemas = anxious / worried
• merasa cemas = to feel anxious

So:

• Saya cemas = I am anxious
• Saya merasa cemas = I feel anxious

In many contexts, they mean almost the same thing. Using merasa makes the emotional experience more explicit.

Usually, no. It normally means my female friend.

That is important because English girlfriend can mean either:

• a female friend
• a romantic partner

In Indonesian, a romantic girlfriend is more commonly:

• pacar saya

So:

• teman perempuan saya = usually my female friend
• pacar saya = my girlfriend in the romantic sense

Context can always affect meaning, but the default reading of teman perempuan saya is non-romantic.

Yes, but the nuance is a little different.

• teman perempuan saya = my female friend
• teman saya perempuan = more like my friend is female or my friend happens to be a woman

The first one feels more like a single noun phrase. The second one feels more descriptive.

In this sentence, teman perempuan saya sounds smoother and more natural.

It sounds neutral to fairly formal.

Why?

• saya is more formal/neutral than aku
• melainkan sounds more formal than many everyday alternatives

A casual version might be:

• Bukan cuma aku yang cemas, teman perempuanku juga.
• Nggak cuma aku yang merasa cemas, teman perempuanku juga.

These mean basically the same thing, but they sound more conversational.

Yes, Indonesian allows some flexibility.

For example, you could say:

• Bukan hanya saya yang merasa cemas; teman perempuan saya juga.
• Bukan hanya saya, melainkan juga teman perempuan saya, yang merasa cemas.

These still mean roughly the same thing.

The key thing is that the sentence must still clearly show the not only X, but also Y relationship.

Saya is the standard polite or neutral first-person pronoun.
Aku is more informal and personal.

So:

• saya = neutral, polite, suitable in writing and general speech
• aku = casual, intimate, everyday speech with friends, family, or in personal contexts

In a sentence with melainkan, using saya fits the overall more formal style. If you changed it to aku, the sentence would sound less formal:

• Bukan hanya aku yang merasa cemas, melainkan juga teman perempuanku.

That is still grammatical, though a bit stylistically mixed because melainkan remains fairly formal.