Está casado desde mayo.

Spanish normally uses estar casado for to be married.

That is because casado is treated as a resulting state or condition: someone got married and now is married. So:

• Está casado = he is married
• Está casada = she is married

Using ser here is not the normal way to express marital status.

Casado is the past participle of casar (to marry), but in this sentence it works like an adjective.

So in Está casado desde mayo, casado describes the person’s state:

• casado = married
• casada = married, feminine
• casados / casadas = married, plural

Because it behaves like an adjective, it agrees with the person it describes in gender and number.

Common forms:

• Está casado = he is married
• Está casada = she is married
• Están casados = they are married / they are married men / a mixed group
• Están casadas = they are married women

So the sentence changes depending on who you are talking about.

Spanish often leaves out subject pronouns when the verb already makes the person clear. This is very normal.

So:

• Está casado desde mayo
• Él está casado desde mayo

Both are possible, but the first is more natural unless you want emphasis or contrast.

Está is the present indicative of estar.

Spanish often uses the present tense for a situation that began in the past and still continues now, especially with desde.

So Está casado desde mayo means the person became married in May and is still married now.

This is different from English, which often prefers has been married since May.

Desde marks the starting point of an action or state that continues up to the present.

So:

• desde mayo = since May

It tells you when the state started.

Compare:

• Está casado desde mayo = He has been married since May.
• Se casó en mayo = He got married in May.

The first focuses on the ongoing state; the second focuses on the event.

In Spanish, months usually appear without an article after prepositions like desde, en, hasta, and so on.

So the normal form is:

• desde mayo
• en mayo
• hasta mayo

You would not normally say desde el mayo here.

In Spanish, names of months are normally written in lowercase.

So:

• mayo
• junio
• septiembre

This is different from English, where May is capitalized.

Yes, but it means something slightly different.

• Se casó en mayo = He got married in May.
  This talks about the event itself.
• Está casado desde mayo = He has been married since May.
  This talks about the state that began in May and continues now.

So both are correct, but they are not interchangeable in every context.

The accent mark shows where the stress goes: es-TÁ.

It also distinguishes está from esta:

• está = is
• esta = this, feminine

So the accent is important for both pronunciation and meaning.

Yes, it is natural and correct.

It clearly means that the person has been married since May. Depending on context, native speakers might also say:

• Lleva casado desde mayo

This also means He has been married since May, with a strong idea of duration.

But your original sentence is perfectly good Spanish.

Yes. By itself, desde mayo just gives the starting point May, but it does not tell you which year unless the context makes it clear.

If needed, Spanish can be more specific:

• desde mayo de este año = since May this year
• desde mayo del año pasado = since May last year

So the basic sentence leaves that detail open unless the conversation already makes it obvious.