Está enamorado desde mayo.

Because Spanish normally uses estar with enamorado to talk about the state of being in love: estar enamorado = to be in love.

Using ser would change the meaning. Es enamorado is not the normal way to say he is in love. If you hear ser enamorado in some contexts, it can suggest something more like being romantic, affectionate, or a person who falls in love easily, not the current emotional state.

So:

• Está enamorado = He is in love
• Es muy enamorado = more like He is very romantic / very amorous

Spanish often leaves out subject pronouns when they are understood from the verb form and the context.

Está is a third-person singular form, so it could mean:

• he is
• she is
• it is
• you are (formal singular, usted)

In this sentence, enamorado is masculine singular, so that strongly suggests a masculine subject, for example:

• He is in love since May
• You are in love since May (said to a man, formal)

If the person were female, it would usually be:

• Está enamorada desde mayo

The correct word is enamorado.

It changes form to agree with the person or thing being described:

• enamorado = masculine singular
• enamorada = feminine singular
• enamorados = masculine plural or mixed group
• enamoradas = feminine plural

So:

• Está enamorado desde mayo. = a male subject
• Está enamorada desde mayo. = a female subject

It is historically the past participle of enamorar (to make someone fall in love / to charm), but in this sentence it works like an adjective.

So in Está enamorado, you can think of it as describing a state, just like:

• Está cansado = He is tired
• Está preocupado = He is worried
• Está enamorado = He is in love

That is why it agrees in gender and number with the subject.

Here desde means since.

It gives the starting point of an action or state that began in the past and continues up to now.

So:

• desde mayo = since May

A useful contrast:

• desde
  • starting point → since / from
• durante or por can relate more to duration in other contexts, but not in the same way here

In this sentence, desde mayo tells you when the state of being in love started.

Because Spanish commonly uses the present tense with expressions like desde to describe something that started in the past and is still true now.

So:

• Está enamorado desde mayo.

naturally means:

• He has been in love since May

This is very common in Spanish. English often prefers the present perfect here, but Spanish usually just uses the present.

A similar example:

• Vive aquí desde 2020. = He has lived here since 2020.

Yes. You usually add de:

• Está enamorado de Ana. = He is in love with Ana.
• Está enamorado de ella. = He is in love with her.

Without de + person/thing, the sentence just means that he is in love, without saying with whom.

They are related, but they are not the same.

• Está enamorado desde mayo focuses on the state: he has been in love since May and still is.
• Se enamoró en mayo focuses on the moment or event: he fell in love in May.

So:

• Se enamoró en mayo y todavía está enamorado. = He fell in love in May and he is still in love.

That shows the difference clearly:

• se enamoró = the change happened
• está enamorado = the resulting state

In standard Spanish, the names of the months are normally written in lowercase, unlike in English.

So Spanish writes:

• mayo
• junio
• septiembre

not:

• Mayo
• Junio
• Septiembre

They are only capitalized if they begin a sentence or are part of a title that follows title-style capitalization rules.

No, not here.

After desde, month names usually appear without an article:

• desde mayo
• desde abril
• desde enero de 2024

So Está enamorado desde mayo is correct and natural.

You may sometimes see articles in other structures, but in this sentence desde mayo is the normal choice.