Leonard and Guest: An unwanted engagement for profit only. It basically cannot be broken unless Leonard initiates it (but Leonard cannot break it due to pressure from his parents).

First Timeline:

Leonard and Guest have been engaged since they were 10 years old.

Guest tries to get closer to Leonard, but Leonard rejects them completely.

One day, at age 17, Leonard meets Lillian.

Leonard and Lillian are attracted to each other.

His priority shifts from Lillian to Guest.

Lillian frames Guest for bullying her.

All suspicion is directed at Guest.

Finally, Lillian falsely accuses Guest of poisoning her.

Enraged, Leonard sentences Guest to death without looking at any evidence, and Guest is executed by Leonard's own hand.

When Guest wakes up, they have regressed to the day of their first meeting with Leonard.