O colega com quem estudo português também vai à aula amanhã.

Because quem is commonly used for people after a preposition.

Here, com = with, so Portuguese needs a structure like:

• com quem estudo português = with whom I study Portuguese

A native English speaker might expect something more like que, but after a preposition, quem is very common when referring to a person.

So:

• o colega que estuda comigo = the classmate who studies with me
• o colega com quem estudo português = the classmate with whom I study Portuguese

Both are natural, but they are built differently.

No. That is not natural Portuguese.

In English, it is normal to leave the preposition at the end:

• the classmate I study Portuguese with

Portuguese normally does not do that here. The preposition stays before the relative word:

• o colega com quem estudo português

So the pattern is:

• preposition + quem
• com quem
• de quem
• para quem

That is the standard structure.

Colega can mean colleague, classmate, or sometimes just peer, depending on context.

In this sentence, because of estudo português and vai à aula, the most natural meaning is probably:

• classmate
• or possibly study partner

So although colega often means colleague in workplace contexts, here it probably means someone from the same course or class.

Portuguese often uses the definite article where English might prefer a possessive like my.

So:

• O colega com quem estudo português...
  can naturally mean something like
• The classmate I study Portuguese with...

Depending on context, English might also say:

• My classmate...
• The classmate...

Portuguese does not always need meu/minha if the person is already identifiable from context.

Estudo is the 1st person singular present of estudar:

• eu estudo = I study

The present tense here expresses a current or regular situation:

• the classmate with whom I study Portuguese

It does not necessarily mean you are studying right this second. It can mean this is an ongoing arrangement or habit.

Because after verbs like estudar, falar, aprender, languages are usually used without an article.

So:

• estudo português
• falo inglês
• aprendo francês

This is similar to English:

• I study Portuguese
• not I study the Portuguese

The word português here means the Portuguese language, not a Portuguese person.

Because à is the contraction of:

• a (the preposition to)
• a (the feminine singular definite article the)

So:

• vai a + a aula → vai à aula

This is required because aula is feminine:

• a aula = the class / the lesson

So:

• vai à aula = goes to class

This accent is important. À is not just a spelling detail here; it shows the contraction.

Not usually. Ir à aula normally means to go to class or to attend class.

So in this sentence:

• também vai à aula amanhã
  means
• is also going to class tomorrow

If you specifically wanted to say to the classroom as a physical room, you would more likely say something like:

• vai para a sala de aula
• vai à sala de aula

But ir à aula is usually about the lesson/class itself, not just the room.

Também means also or too, and its position is fairly flexible, though some positions sound more natural than others.

In your sentence:

• O colega com quem estudo português também vai à aula amanhã.

This is a very natural placement. It means:

• The classmate I study Portuguese with is also going to class tomorrow.

It can often appear near the verb or before the part it relates to. For example:

• Também vai à aula amanhã. = He/She is also going to class tomorrow.

In this sentence, também most naturally adds the idea that this person, like someone else already mentioned, is going too.

Because adverbs of time are often placed at the end in Portuguese, and that sounds very natural here.

• vai à aula amanhã = is going to class tomorrow

You could move amanhã earlier in some cases, but the end position is simple and common.

For example:

• O colega com quem estudo português vai amanhã à aula.

This is possible, but the original sentence sounds more natural for most everyday contexts.

Not exactly. Vai is the present tense of ir:

• ele/ela vai = he/she goes / is going

But Portuguese, like English, often uses the present tense with a future time expression:

• vai à aula amanhã = literally goes to class tomorrow

In natural English, we usually translate that as:

• is going to class tomorrow
• or will go to class tomorrow

So the future meaning comes mainly from amanhã.

As written, O colega refers to a male classmate/colleague, because o is masculine.

For a female, you would say:

• A colega com quem estudo português também vai à aula amanhã.

A useful detail: colega has the same form for masculine and feminine, so the article shows the gender:

• o colega = male classmate/colleague
• a colega = female classmate/colleague

Yes. It is a relative clause describing which colega we mean.

So the sentence is structured like this:

• O colega = the classmate
• com quem estudo português = with whom I study Portuguese
• também vai à aula amanhã = is also going to class tomorrow

So the middle part identifies the person more precisely:

• not just the classmate
• but the classmate with whom I study Portuguese

Yes, it is completely natural and correct in European Portuguese.

A few especially natural features are:

• com quem for a person after a preposition
• vai à aula with the correct contraction
• também in a normal position
• amanhã at the end

So this is a good model sentence for formal or neutral everyday Portuguese in Portugal.