sayonara wo iu no ha muzukasikatta.

A helpful breakdown is:

• さよなら = goodbye
• を = marks the thing being said
• 言う = to say
• の = turns the verb phrase into a noun-like unit
• は = marks that noun-like unit as the topic
• 難しかった = was difficult

So the structure is basically:

• [さよならを言う] = to say goodbye
• [さよならを言う の] = saying goodbye
• [さよならを言う の は] = as for saying goodbye
• 難しかった = was difficult

Natural English: Saying goodbye was difficult.

Here, の is being used as a nominalizer. That means it turns a verb phrase into something that behaves like a noun.

• 言う = to say
• 言うの = saying / the act of saying

So:

• さよならを言う = to say goodbye
• さよならを言うの = saying goodbye

This is very common in Japanese. It lets an action become the topic or subject of a sentence.

Because the whole action さよならを言うの is the topic of the sentence.

Japanese often does this:

• [verb phrase] の は ...
• As for [doing something], ...

So here:

• さよならを言うのは難しかった
• As for saying goodbye, it was difficult

The は is not marking さよなら by itself. It is marking the whole phrase さよならを言うの.

難しかった is the past form of 難しい.

• 難しい = difficult
• 難しかった = was difficult

This means the speaker is talking about a past situation: at that time, saying goodbye was difficult.

If you said:

• さよならを言うのは難しい

  that would mean Saying goodbye is difficult or It is difficult to say goodbye, in a more general or present-time sense.

Great question. With 言う, both を and と can appear, but they are used differently.

In this sentence:

• さよならを言う = to say goodbye

Here, さよなら is treated almost like the content or expression being uttered, and を言う is a very common pattern with words like greetings and fixed expressions.

Examples:

• ありがとうを言う = to say thank you
• 文句を言う = to complain / say complaints
• さよならを言う = to say goodbye

What about と?

と is often used for direct quotations or exact spoken content:

• 「さよなら」と言う = to say goodbye

This sounds more like quoting the actual words.
So:

• さよならを言う = say goodbye
• 「さよなら」と言う = say “goodbye”

Both are possible, but を言う is very natural when talking about the act of offering a farewell.

Yes:

• さよならを言うことは難しかった

This is also grammatical and means basically the same thing.

Difference:

• の often feels a little more direct, immediate, or conversational.
• こと can feel a little more formal or abstract.

In many cases, either one works. In this sentence, の sounds very natural.

Japanese often leaves the subject unstated when it is understood from context.

So さよならを言うのは難しかった could mean:

• It was difficult for me to say goodbye
• It was difficult for him/her/them to say goodbye
• Saying goodbye was difficult

Context tells you who is involved.

If the speaker wanted to make it explicit, they could say:

• 私はさよならを言うのが難しかった
  or
• 私にとって、さよならを言うのは難しかった

But in natural Japanese, leaving it out is very common.

Not always. さよなら is a real and common word, but its nuance can be stronger or more final than English bye in some situations.

Depending on context, Japanese speakers may also say things like:

• じゃあね
• またね
• バイバイ
• 失礼します

So in this sentence, さよなら may sound a bit emotional, serious, or final, which fits well with 難しかった.

That is one reason the sentence can feel emotionally meaningful: saying さよなら may suggest a more important farewell, not just a casual see you.

Because it is part of a noun-modifying phrase before の.

Japanese often uses the plain form before の:

• 食べるの = eating / the act of eating
• 行くの = going
• 言うの = saying

So さよならを言うの literally means the act of saying goodbye.

The verb does not need to be in -ます form here. In fact, 言いますのは would not be natural in this sentence.

Normally, Japanese is written without spaces:

• さよならを言うのは難しかった。

Spaces are often added in teaching materials to help beginners see the parts more clearly.

So the spaced version is useful for learning, but standard Japanese writing would not include those spaces.

Yes, very much so.

Even though the grammar is simple, さよならを言うのは難しかった can sound quite emotional because:

• さよなら can suggest a serious farewell
• 難しかった shows emotional difficulty
• the sentence focuses on the act itself: saying goodbye was hard

So depending on context, it might mean not just that it was technically hard to say the words, but that it was emotionally painful.

Sometimes learners expect:

• さよならを言うのが難しかった

This is also very natural.

Difference:

• のは難しかった presents saying goodbye as the topic: As for saying goodbye, it was difficult
• のが難しかった focuses more directly on what was difficult: What was difficult was saying goodbye

In many situations, both are possible and the meaning is very close.
Your sentence with は is completely natural and gives a slightly topical or contrastive feel.