Analysis:
This quatrain by Saadi Shirazi is a poignant expression of heartbreak and betrayal. Let's break down each line:

Line 1: آن یار که عهدِ دوستاری بشکست

"That friend who broke the promise of friendship"
The speaker is addressing a former friend who has betrayed their trust by breaking a promise.

Line 2: می‌رفت و منش گرفته دامان در دست

"Was leaving, and I had grasped their garment"
The speaker is desperately trying to hold onto the departing friend, symbolizing their desire to keep the relationship alive.

Line 3: می‌گفت دگرباره به خوابم بینی

"They said, 'You will see me again in your dreams'"
The departing friend offers a hollow promise of future reunion, perhaps to ease the pain of separation.

Line 4: پنداشت که بعد از آن مرا خوابی هست

"Thinking I would have any sleep after that"
The speaker expresses their deep sorrow and despair, suggesting that they will be unable to sleep due to their heartache.

Themes explored in the quatrain:

Betrayal and heartbreak: The central theme is the pain of betrayal and the subsequent heartbreak.
The fragility of relationships: The quatrain highlights the fragility of human connections and the ease with which they can be broken.
The power of hope: The departing friend's promise of future reunion offers a glimmer of hope, but it is ultimately shattered.

In essence, this quatrain is a powerful and evocative expression of the pain of loss and the fragility of human relationships. It captures the universal experience of heartbreak and the longing for connection.