Я боюсь снова простудиться, поэтому пью тёплый чай с мёдом.

Because the verb is бояться — to be afraid. It is a reflexive verb, so in the I form it becomes боюсь.

• бояться = to be afraid
• я боюсь = I am afraid

The -сь / -ся ending is part of the verb and cannot be dropped here.

In Russian, бояться is very often followed by an infinitive when you are afraid of doing something or of something happening.

So:

• боюсь простудиться = I’m afraid of catching a cold

This is very similar to English I’m afraid to... or I’m afraid of... happening, but Russian commonly uses the infinitive in this structure.

Compare:

• Я боюсь летать. = I’m afraid to fly.
• Я боюсь опоздать. = I’m afraid of being late.

Because простудиться means to catch a cold, while простудить usually means to chill something / cause something to become cold.

So:

• простудиться = to catch a cold
• простудить = to chill, to expose something or someone to cold

For example:

• Я простудился. = I caught a cold.
• Я простудил горло. = I got my throat chilled / I messed up my throat from the cold.

In your sentence, the speaker is afraid that they themselves will catch a cold, so the reflexive verb простудиться is the correct choice.

Because the sentence refers to catching a cold as a single event. Russian often uses the perfective infinitive after бояться when the speaker fears that something may happen once.

• простужаться would suggest a repeated or ongoing process
• простудиться focuses on the result: to come down with a cold

So боюсь снова простудиться means I’m afraid of catching a cold again, not I’m afraid of being in the process of catching colds.

Снова means again.

It is placed before the infinitive because it modifies that action:

• снова простудиться = to catch a cold again

That is the most natural position here. Russian word order is flexible, but this placement clearly ties again to the verb.

Possible variations may exist in other contexts, but боюсь снова простудиться is the standard, natural phrasing.

Because поэтому connects two clauses:

• Я боюсь снова простудиться
• поэтому пью тёплый чай с мёдом

In writing, Russian normally uses a comma before поэтому when it means therefore / so / that’s why and links one clause to another.

So the structure is:

• I’m afraid of catching a cold again, so I drink warm tea with honey.

Russian often omits the subject pronoun when it is already clear from the verb ending or from context.

Here:

• пью already means I drink
• the subject is obviously the same я from the first clause

So поэтому пью... is perfectly natural. You could say поэтому я пью..., but it is not necessary.

Russian does this much more often than English.

The infinitive is пить — to drink.

Its present-tense forms are somewhat irregular:

• я пью
• ты пьёшь
• он / она пьёт
• мы пьём
• вы пьёте
• они пьют

So пью may look quite different from пить, but it is just the normal I drink form of that verb.

Тёплый means warm.

The letter ё shows the pronunciation clearly:

• тёплый = pronounced with yo

In many Russian texts, especially informal ones, ё is often written as е, so you may also see теплый. But the correct pronunciation is still тёплый.

For learners, it is very helpful to remember the ё here.

Because the preposition с in the meaning with usually requires the instrumental case.

• nominative: мёд
• instrumental: мёдом

So:

• чай с мёдом = tea with honey

This is a very common pattern:

• кофе с молоком = coffee with milk
• бутерброд с сыром = sandwich with cheese

Sometimes, but they are not identical.

• поэтому = therefore / so / that’s why
• из-за этого = because of this / due to this

In your sentence, поэтому is the most natural connector because the second clause is a result of the first:

• I’m afraid..., so I drink...

Из-за этого is possible in some contexts, but it sounds a bit heavier and less natural here.

Yes, Russian word order is flexible, but different orders may sound more or less natural depending on what you want to emphasize.

The original sentence is neutral and natural:

• Я боюсь снова простудиться, поэтому пью тёплый чай с мёдом.

You could also say:

• Я снова боюсь простудиться...

But that can shift the emphasis and may sound like I’m again afraid, rather than I’m afraid of catching a cold again.

So in this sentence, боюсь снова простудиться is the clearest and most natural way to express the idea.