Preciso aceitar a realidade.

Yes. In Portuguese, the verb ending often shows who the subject is, so the subject pronoun is frequently omitted.

• Preciso = I need
• Eu preciso = I need too, but with extra emphasis or clarity

So Preciso aceitar a realidade is a perfectly natural way to say I need to accept reality.

Preciso is the 1st person singular present tense of precisar.

• precisar = to need
• preciso = I need

So the sentence is in the present tense: I need to accept reality.

Because after precisar, Portuguese commonly uses another verb in the infinitive to express need to do something.

Pattern:

• precisar + infinitive

Examples:

• Preciso estudar. = I need to study.
• Preciso descansar. = I need to rest.
• Preciso aceitar a realidade. = I need to accept reality.

This is very similar to English need to + verb.

Portuguese often uses the definite article where English might not.

So:

• a realidade = reality

Even though English often says just reality, Portuguese commonly prefers a realidade in this kind of sentence.

Compare:

• Aceitar a realidade = accept reality
• Enfrentar a verdade = face the truth

Using the article here sounds natural and standard.

Yes, absolutely. That is also correct.

The difference is mainly style and emphasis:

• Preciso aceitar a realidade. = more neutral, very natural
• Eu preciso aceitar a realidade. = adds emphasis to I

You might include eu if:

• you want contrast: Eu preciso aceitar, mas ele não
• you want emphasis
• you want to be especially clear

Not always. Precisar can be used in two common ways:

1. precisar + infinitive

   • Preciso aceitar a realidade.
   • Preciso dormir.

2. precisar de + noun

   • Preciso de ajuda. = I need help.
   • Preciso de dinheiro. = I need money.

So in your sentence, since aceitar is a verb, there is no de.

Grammatically, yes, but it sounds more formal or less common in everyday speech.

In normal Brazilian Portuguese, people much more often say:

• Preciso aceitar a realidade.

Necessitar exists, but it is less common in casual conversation.

Yes. Tenho que aceitar a realidade is also very common and natural.

The difference is subtle:

• Preciso aceitar a realidade = I need to accept reality
• Tenho que aceitar a realidade = I have to accept reality

In many everyday situations, they are quite close in meaning.
Tenho que can sometimes sound a little stronger or more like obligation, while preciso can sound more like necessity.

As a verb in Preciso aceitar a realidade, preciso means I need.

But preciso can also be an adjective meaning precise or accurate:

• um valor preciso = an exact value

So context matters.

In pronunciation, Brazilian Portuguese usually says preciso roughly like preh-SEE-zoo.
The s between vowels sounds like a z sound in most Brazilian accents.

Yes, very natural. It sounds like something a native speaker would say.

It can express:

• personal reflection
• emotional acceptance
• resignation
• maturity

It is a simple, idiomatic sentence in Brazilian Portuguese.

Usually the normal order is:

• Preciso aceitar a realidade.

That is the most natural version.

You could change the order in special contexts for emphasis, but it would sound more marked or literary. For everyday speech, keep the standard order:

• verb: Preciso
• infinitive: aceitar
• object: a realidade

Here are a few natural variations:

• Eu preciso aceitar a realidade. = same meaning, with explicit I
• Preciso encarar a realidade. = I need to face reality
• Tenho que aceitar a realidade. = I have to accept reality
• Preciso aceitar os fatos. = I need to accept the facts

These all sound natural, but aceitar a realidade is a very standard and common way to express the idea.