Я люблю чай, а вот мой брат любит кофе.

Because the verb changes depending on the subject.

The infinitive is любить = to love / to like.

Here it is conjugated:

• я люблю = I like
• ты любишь = you like
• он / она любит = he / she likes

So:

• Я люблю чай = I like tea
• мой брат любит кофе = my brother likes coffee

The ending tells you who is doing the action.

Because Russian does not use a separate word like English to in this kind of sentence.

In English, I like tea already has no to, but learners often ask this because some languages say something more like To me tea is pleasing. Russian does not do that here.

Russian simply uses:

• я люблю = I like / I love
• чай = tea

So Я люблю чай is a direct, normal way to say I like tea.

А often means something like and, while, or but when contrasting two ideas.

In this sentence, it sets up a contrast:

• Я люблю чай, а ... мой брат любит кофе.
• I like tea, while my brother likes coffee.

Вот adds emphasis or draws attention, something like:

• as for
• now
• on the other hand
• meanwhile

So а вот мой брат gives a feeling like:

• but my brother, on the other hand, likes coffee
• whereas my brother likes coffee

It is not a word-for-word translation thing; it is more about tone and emphasis.

Both can sometimes translate as but, but they are not always the same.

• но = a stronger, more direct contradiction
• а = contrast or comparison

Here the sentence is not saying one fact cancels the other. It is just contrasting preferences:

• I like tea, whereas my brother likes coffee.

That is why а sounds natural.

If you used но, it would sound more like a stronger opposition, which is less natural here.

Russian has no articles.

So Russian does not have separate words for:

• a
• an
• the

That means:

• чай can mean tea or the tea, depending on context
• брат can mean brother or the brother, depending on context

In this sentence, the meaning is understood from context:

• мой брат = my brother
• чай = tea
• кофе = coffee

Yes, they are objects, so they are in the accusative case.

But here the forms happen to look the same as the dictionary form.

Why?

чай

Чай is masculine and inanimate.
For masculine inanimate nouns, the accusative is the same as the nominative.

• nominative: чай
• accusative: чай

кофе

Кофе is usually treated as an indeclinable noun, so its form does not change here.

So although both words are functioning as direct objects, they stay:

• люблю чай
• любит кофе

Because мой брат is the subject of the second clause.

In:

• мой брат любит кофе

the brother is the person who likes coffee, so he must be in the nominative case:

• мой брат = my brother

If he were the object, then you might see a different form, such as моего брата in some contexts.

So here:

• мой брат = subject
• кофе = object

Yes. Russian word order is more flexible than English word order.

The neutral order here is:

• Я люблю чай, а вот мой брат любит кофе.

But Russian can move words around for emphasis or style. For example:

• Чай я люблю, а вот мой брат любит кофе.
• Я чай люблю, а вот мой брат — кофе.

These versions can sound more emphatic or contrastive.

Still, the original sentence is a very natural, standard way to say it.

Because кофе is a borrowed word with unusual behavior.

In standard Russian, кофе is traditionally masculine:

• чёрный кофе = black coffee
• горячий кофе = hot coffee

Even though many nouns ending in -е are neuter, кофе is a well-known exception.

Also, it is usually indeclinable, which means its form often does not change across cases.

So in this sentence:

• любит кофе

the form stays кофе.

It can mean both, depending on context.

• With people, любить often means to love.
• With things, foods, activities, or general preferences, it often means to like.

So here:

• Я люблю чай does not sound overly emotional.
• It simply means I like tea.

Russian often uses любить where English would normally say like.

The comma separates two clauses:

• Я люблю чай
• а вот мой брат любит кофе

Each clause has its own subject and verb:

• я люблю
• брат любит

In Russian, clauses joined by а are normally separated by a comma.

So the comma is required here.

Without вот, the sentence would still be correct:

• Я люблю чай, а мой брат любит кофе.

This simply means:

• I like tea, and/as for my brother, he likes coffee
• I like tea, while my brother likes coffee

Adding вот makes the contrast a little more noticeable and conversational:

• Я люблю чай, а вот мой брат любит кофе.

So вот is not required for grammar, but it adds emphasis.

Yes, in some contexts.

Russian often omits possessive words like my when the meaning is obvious. So depending on context, someone might say:

• Я люблю чай, а брат любит кофе.

But мой брат is very natural if the speaker wants to be clear or slightly more explicit.

So:

• брат = possible if context is clear
• мой брат = clear and fully natural