When it’s over, it’s over. It’s like in Aleks Syntek’s song "Intocable" (Untouchable), where the poor guy was dumped and ends up consoling himself by singing:

Si en el juego del amor

If in the game of love

ahora soy el perdedor

now I'm the loser

debo salir adelante

I must move on

Captions 4-6, Aleks Syntek - Intocable

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In Spanish, when we want to express an obligation or a responsibility, we use the verb deber, properly conjugated of course, followed by the infinitive of the verb denoting the action that we must carry out.

Debo hacer mi tarea.
I must do my homework.

Debiste haberme avisado.

You should have warned me OR you should have told me in advance.

"Deber + infinitive" vs. "tener que + infinitive"

"Deber + infinitive" tends to imply a sense of *internal* obligation, whereas "tener que + infinitive," which is extremely common and very close in meaning, tends to convey a sense of *external* obligation.

Emilio debe levantar su ropa sucia.
Emilio should pick up his dirty clothes. (For his own good and that of the household.)

Emilio tiene que levantar su ropa sucia.
Emilio must/has to pick up his dirty clothes. (Or his mother will ground him.)

So any time you want to express a sense of responsibility or obligation, especially one that stems of an internal sense of duty, just conjugate the verb deber and then add the infinitive of the action verb.
 

Sé que no será fácil pero debo confesarle la verdad.

I know it won't be easy but I must confess the truth.

"Deber de + infinitive"

But hold on there for a minute! A little later in the song, Syntek changes the syntax around considerably by singing:

Debes confundida estar

You must be confused

Caption 13, Aleks Syntek - Intocable

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Actually two things are happening simultaneously, so you should be patient and bear with us! (¡Debes ser paciente y aguantarnos!)

First of all, the syntax. Normally, one would say, sing or write:

Debes estar confundida. 
You must be confused.

He turned the sentence on its head so this line Debes confundida estar would rhyme with the next one:

Terminar por terminar
To break up for the sake of breaking up

The second thing here is a finer point of Spanish grammar. When one wants to give the listener or reader the idea of probability, one also uses the verb deber, but before the infinitive, one should also include the preposition de. Technically, this is what Aleks Syntek should have sung:
 

Confundida debes de estar.
You must be [probably are] confused.

Denisse Guerrero makes the opposite error (adding "de" where she should have left it out) when she sings "Lo siento, niño, debo de partir" (I'm sorry, boy, I must leave) in line 27 of the Belanova video "Niño":

Lo siento, niño, debo de partir

I'm sorry, boy, I must leave

Caption 27, Belanova - Niño

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Strictly speaking, she should have simply sung "debo partir" (I must leave). But we are not out to pick on pop stars*!

A confusing matter

Many native speakers, both in Spain and Latin America, are not consciously aware of this difference and tend to sweep it under the rug, which is unfortunate because there is a huge difference between responsibility or obligation, and probability.

Check out these two sentences, which mean two different things:
 

Aleks Syntek debió de entender la diferencia.
Aleks Syntek probably understood the difference. (That is the most likely scenario.)

Aleks Syntek debió entender la diferencia.
Aleks Syntek should have understood the difference. (Because it was his obligation or responsibility.)

See what we mean? Let’s chalk it up to the poor girl’s unfortunate decision to leave him, when debió quedarse con él (“she should have stayed with him”). But there’s no accounting for taste.

*At least one pop diva wasn't daydreaming during her grammar lessons. Natalia Oreiro, as eloquent as she is lovely, correctly uses "deber de + infinitive" when she says:

Más que sentirme mal yo,

More than feeling badly myself,

imagínate cómo se deben de sentir ellos.

imagine how they must feel.

Captions 40-41, Biografía - Natalia Oreiro

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That's it for today. We hope you find this lesson useful and we invite you to send us your comments and suggestions.