Me faltas mucho cuando estás lejos.

Because Spanish often expresses this idea with a different structure from English.

With faltar, the person who feels the absence is usually the indirect object, so me means to me. A very literal way to think of me faltas is:

you are lacking to me

That sounds unnatural in English, but it helps explain the grammar.

So:

• me faltas = I miss you / you are absent for me
• te falto = you miss me
• nos faltáis = we miss you all

In Spain, te echo de menos is often more common in everyday speech for I miss you, but me faltas is still understandable and can sound emotional or poetic.

Because me is the object pronoun, not the subject.

In this sentence, you are the grammatical subject, even though in English we would say I miss you.

So the parts are:

• me = to me
• faltas = you are lacking / you are missed
• implied subject = tú

Spanish is using the same kind of pattern as verbs like gustar:

• Me gustas = I like you
  literally: you are pleasing to me
• Me faltas = I miss you
  literally: you are lacking to me

So yo would not fit here, because yo is a subject pronoun, and here I is not the grammatical subject.

Because the verb has to agree with the subject, and the subject here is an implied tú.

So:

• tú faltas
• él/ella falta
• vosotros faltáis
• ellos faltan

In me faltas mucho, the hidden subject is tú, so the correct form is faltas.

Compare:

• Me faltas tú. = I miss you.
• Me falta Ana. = I miss Ana.
• Me faltan mis amigos. = I miss my friends.

The verb changes depending on who or what is being missed.

No. Faltar has several related meanings, all connected to the idea of absence or lack.

Common uses include:

• to be missing / lacking
  Falta sal. = Salt is missing / We need salt.
• to be absent
  Hoy falta Juan. = Juan is absent today.
• to miss someone in a more literal or emotional sense
  Me faltas mucho. = I miss you a lot.

So in this sentence, faltar is being used in the emotional sense: someone’s absence is strongly felt.

Because mucho is modifying the verb, not an adjective or adverb.

Here mucho means a lot:

• Me faltas mucho = I miss you a lot

Use muy before adjectives or adverbs:

• muy lejos = very far
• muy triste = very sad

Use mucho to express quantity or degree with verbs:

• Te quiero mucho = I love you a lot
• Te echo mucho de menos = I miss you a lot
• Me faltas mucho = I miss you a lot

So muy would be wrong here.

Because estar is used for location and states, while ser is not used with lejos in this way.

Estar lejos means to be far away:

• Madrid está lejos.
• Cuando estás lejos...

This is about where someone is, or about their distance from the speaker, so estar is the correct verb.

Ser would not work here because being far away is not treated as an essential identity; it is a location or situation.

It means when you are far away or when you’re away.

A few points:

• cuando = when
• estás = you are
• lejos = far away

So the whole clause gives the condition or situation in which the feeling happens:

Me faltas mucho cuando estás lejos.
= I miss you a lot when you’re far away.

It can suggest either:

• a general truth: whenever you’re away, I miss you
• a present situation: I miss you a lot now that you’re away

Spanish present tense can cover both kinds of meaning depending on context.

Yes. That word order is completely natural.

Spanish allows some flexibility in word order, especially with time clauses like cuando estás lejos.

Both versions work:

• Me faltas mucho cuando estás lejos
• Cuando estás lejos, me faltas mucho

The difference is mainly emphasis:

• starting with Me faltas mucho puts the emotional statement first
• starting with Cuando estás lejos highlights the situation first

It is understandable, correct, and expressive, but it is not the most neutral everyday choice in most of Spain.

In Spain, the most common everyday phrase is usually:

• Te echo de menos. = I miss you.
• Te echo mucho de menos. = I miss you a lot.

Me faltas mucho can sound more emotional, intimate, or literary. It suggests that the person’s absence leaves a real gap in your life.

So if you want the most standard colloquial option in Spain, use te echo de menos. If you want something a bit more heartfelt, me faltas mucho works well.

Yes, and it is very close in meaning, though not identical in tone.

• Me faltas mucho = I miss you a lot
• Me haces mucha falta = I really need you / your absence is strongly felt

Me haces mucha falta often emphasizes that the person is important, necessary, or deeply missed in your daily life. It can sound a bit stronger in terms of emotional need.

So:

• Te echo de menos = common everyday I miss you
• Me faltas = your absence affects me
• Me haces mucha falta = I really feel the lack of you

Because Spanish often leaves subject pronouns out when the verb already shows who the subject is.

Here faltas and estás both clearly indicate tú, so tú is unnecessary:

• Me faltas mucho cuando estás lejos.

You could add tú for emphasis:

• Tú me faltas mucho cuando estás lejos.

But normally Spanish sounds more natural without it unless you want contrast, emphasis, or emotional focus.