Если у меня есть груша и яблоко, мне уже не нужен сладкий десерт.

Russian usually expresses possession with the pattern:

• у + genitive pronoun/noun + есть
• literally something like by me there is

So:

• у меня есть груша = I have a pear
• у меня есть яблоко = I have an apple

This is much more natural in Russian than using иметь. The verb иметь does exist, but in everyday speech it is much less common for ordinary possession.

So Если у меня есть груша и яблоко... is the normal way to say If I have a pear and an apple...

After у, Russian uses the genitive case.

The pronoun я changes like this:

• я = I
• меня = me / of me

So:

• у меня literally means at me / by me
• in natural English, that becomes I have

This is just part of the standard Russian possession structure:

• у меня есть
• у тебя есть
• у него есть
• etc.

They are in the nominative case because they are the things that exist / are present in the possession structure.

In у меня есть груша и яблоко, the nouns naming the possessed items are normally nominative:

• груша = pear
• яблоко = apple

Compare:

• У меня есть книга. = I have a book.
• У меня есть брат. = I have a brother.

So the pattern is:

• у + possessor in genitive
• есть
• thing possessed in nominative

Because the structure with нужен / нужна / нужно / нужны works with the dative case for the person who needs something.

So:

• мне нужен десерт = I need a dessert
• literally: to me, a dessert is needed

That is why Russian uses:

• мне = to me not
• я = I

This is a very common pattern:

• мне нужен... = I need...
• тебе нужна... = you need...
• ему нужно... = he needs...

No, нужен is not a normal verb like English need.

It is the short form of the adjective нужный and means something like:

• needed
• necessary

So мне уже не нужен сладкий десерт literally means:

• A sweet dessert is no longer needed for me

Natural English:

• I no longer need a sweet dessert
• I don’t need a sweet dessert anymore

This is a very common Russian way to express need.

Because нужен agrees with десерт.

Десерт is:

• masculine
• singular

So the form must also be:

• нужен = masculine singular

Compare:

• мне нужен десерт = I need a dessert
• мне нужна груша = I need a pear
• мне нужно яблоко = I need an apple
• мне нужны яблоки = I need apples

In the sentence, the thing being described as needed or not needed is сладкий десерт, so masculine singular нужен is correct.

That is the normal word order with this construction:

• мне не нужен десерт
• тебе не нужна книга
• ему не нужно время

The negative particle не goes directly before нужен / нужна / нужно / нужны.

So:

• мне уже не нужен сладкий десерт = I no longer need a sweet dessert

You could move words around for emphasis in Russian, but this order is the most neutral and natural.

Уже usually means already, but in negative sentences it often translates naturally as:

• no longer
• anymore

So:

• мне уже не нужен сладкий десерт

literally:

• to me already not needed sweet dessert

natural English:

• I no longer need a sweet dessert
• I don’t need a sweet dessert anymore

So уже adds the idea that this was perhaps needed or wanted before, but now that has changed.

Because the sentence begins with a subordinate clause introduced by если = if.

Structure:

• Если у меня есть груша и яблоко, = If I have a pear and an apple,
• мне уже не нужен сладкий десерт. = I no longer need a sweet dessert.

In Russian, subordinate clauses are separated by commas, including clauses with если.

So the comma is required.

Sometimes in Russian, есть can be omitted in casual speech when possession is obvious from context, but here у меня есть is the clearest and most standard form.

Compare:

• У меня есть груша и яблоко. = I have a pear and an apple.
• У меня груша и яблоко. = possible in conversation, but more like I’ve got a pear and an apple / As for me, there’s a pear and an apple

For learners, it is best to keep есть in this kind of sentence.

The singular here is natural because it means a sweet dessert in a general sense.

• мне уже не нужен сладкий десерт = I don’t need a sweet dessert anymore

It does not necessarily mean one specific dessert; Russian often uses the singular for a general idea like English a dessert.

A plural version would mean something different:

• мне уже не нужны сладкие десерты = I no longer need sweet desserts

That sounds broader and more general, as if talking about sweet desserts as a category.

That is useful as a learning aid, but not as normal English.

A very literal breakdown is:

• если = if
• у меня = by me / at me
• есть = there is / there are
• груша и яблоко = a pear and an apple

So yes, the internal logic is something like:

• If by me there is a pear and an apple...

But the correct natural English translation is:

• If I have a pear and an apple...

Literal glosses can help you understand the grammar, but you should not use them as final translations.

Not really a major grammatical reason. Both orders are possible.

• груша и яблоко
• яблоко и груша

The choice can depend on rhythm, emphasis, or just the speaker’s preference.

So the sentence would still be grammatical if the order were reversed:

• Если у меня есть яблоко и груша, мне уже не нужен сладкий десерт.

The meaning stays basically the same.