Buenas tardes A,

The usage of the imperfect tense, or pretérito imperfecto in Spanish is multifaceted, serving to convey various nuances of past actions or states.

Let's delve into each of your queries to explain why the imperfect tense is chosen in these contexts:

1. Why is imperfecto used in "Pues que me apetecía"?

   The imperfect tense is used here ("me apetecía") to express a state of mind or a desire in the past that does not have a definite beginning or end. It suggests that at that moment, the speaker felt like doing something, without implying that this feeling was permanent or had a specific duration. It emphasizes the state or feeling rather than its completion.

2. Why use imperfecto in "y entre ellos había una pareja de jóvenes"?

   The imperfect "había" is employed to describe a scene or a situation that was ongoing at a specific moment in the past. It sets the background or provides a description of circumstances without focusing on the start or finish of the action. Even if the couple was there only at that time, the imperfect gives a description of the scene as it was unfolding, without implying repetition or habituality.

3. Why use imperfecto in "¡No me lo podía creer!"?

   The use of "podía" in the imperfect tense reflects an action or state that was ongoing at a specific moment in the past, here conveying the speaker's disbelief or amazement. It suggests that the disbelief was not a one-time reaction but a state of mind that persisted over some time during the moment of realization.

4. The usage of the imperfect in the sentence about the photo session:

   The imperfect tense here is used to describe ongoing actions or states in the past ("había un hombre haciendo fotos y un chico con un foco"). These descriptions provide background information about the scene, contributing to the narrative by setting the stage for what the speaker would later understand. It's about creating a picture of the ongoing situation rather than indicating sequences of completed actions.

5. Why use the imperfect in "Estoy segura de que estaban muertos de frío"?

   The choice of "estaban" (were feeling cold) in the imperfect tense suggests a temporary condition that was experienced during the moment under discussion. It does not necessarily imply that being cold was a one-time occurrence but rather describes their state at that time without indicating when this feeling started or ended.

6. Why not use "llevaron" in "El solo llevaba un bañador y ella un bikini"?

   The imperfect "llevaba" is used to describe what someone was wearing, which is a temporary state or condition at a given moment in the past. Using the imperfect here emphasizes the attire as part of the scene's description, without suggesting that the action of wearing those items had a clear beginning or end point during the event.

In each of these instances, the imperfect tense serves to paint a vivid picture of past states, ongoing actions, or habitual occurrences without confining them to specific points in time. It allows the narrative to flow more naturally, offering depth and context to the described scenes or states of being.

Saludos

Silvia