Of Promises & Paper Airplanes can be used as a solo journaling RPG or as a play-by-post RPG between two or more players. 

Here is a simple guide:

PROLOGUE: Set the scene, Lover. Describe the Meeting Place and your Task.
 
EIGHT ENCOUNTERS:
• Describe the Present. 
• Roll for Time Skip*, Promise and Outcome. 
• Describe the Past using all the given prompts.
* Time Skip will only be rolled Second Encounter onwards.
 
EPILOGUE: Set the scene, Beloved. Describe the reunion at the Meeting Place. Review your Relationship.

And here is an example: 

PROLOGUE

Isaiah dela Torre sits alone in a café, a walking distance from the Departures. He had asked Alessa to meet him there before she went. And now, he waits for her to arrive.

He fidgets with the receipt and before he knew it, he found himself folding a paper airplane. They used to do this back in elementary, just passing messages in the form of paper airplanes.

This will be his last message for her.

RELATIONSHIP: 8

FIRST ENCOUNTER

Dice Rolls: 5, 1
Promise (5): Of fun and happiness
Outcome (1): You break your promise

Alessa Andrada taps her foot as she waits for the cab to arrive. She promised to meet with Isaiah at 2:00 pm and it is now nearly 4:00. She groans.

This has happened before, hasn't it? She had a terrible habit of running late. The worst of it was back in high school.

"Let's go to the fair together, okay? Just you and me. We'll have fun!"

His eyes sparkled as he nodded. "Yeah, let's go!"

She couldn't recall what happened, just that she arrived at the fair three hours later than they had planned. She even considered not showing up entirely. Yet there he was, sitting near the food stalls, a handful of unused tickets in his hands.

"Why are you still here?" she whispered, unable to look at him. "You could've — should've — left. You know that, right?"

"Yes."

"Well? Why didn't you?"

He smiled softly. "It's okay. I'll always wait for you."

RELATIONSHIP: 7

SECOND ENCOUNTER

Dice Rolls: 2, 7, 6
Time Skip (2): A month passes
Promise (7): Of family and home
Outcome (6): You kept your promise

Isaiah continues folding the receipt.

She's running late again, just as always. And like the fool that he is, he finds himself waiting again and again and again. He should've seen the red flags as early as high school. Or maybe he already did. He just chose to ignore them.

A month had passed and Alessa still hadn't explained what happened during the fair. Isaiah never brought it up and believed that it won't ever be. That is, until she approached him one afternoon and said, "I'm sorry."

"Huh?"

"For the fair. I invited you and didn't show up."

"Oh no, it's okay! Besides, you did show up eventually. And we still got to check out the stalls."

Silence. "Why are you so nice to me?"

"Because we're friends?"

She sighed. "You'll get tired of me one day. You'll realize that I'm not a very good friend or person—"

"I don't think so," he interrupted. "You're like family to me. I'll always be around, I promise."

He kept that promise, didn't he? For the past ten years, he has always been there for her. But now... Now, perhaps it is time to break it.

RELATIONSHIP: 7