Possible Animal Ownership Dispute

Location: Guam, USA

My fiancée and I are dealing with a possible cat ownership dispute and are trying to understand what our legal options might be.

A few years ago, we lived with another couple. While living together, we found a stray cat and all agreed to take him in. Everyone contributed to his care at different points, including vet visits. Later, we discussed my fiancée and I taking ownership of the cat, and after multiple conversations, we reached a verbal agreement that he would permanently stay with us.

Based on that agreement, my fiancée paid to have the cat microchipped in her name and also paid for him to be neutered.

After a falling out between the households, we moved out. When we contacted them to arrange picking up the cat, they informed us that they had changed their minds and would be keeping him. They stated that the decision was based on the friendship deteriorating and that they no longer wanted to follow through with the original agreement.

The cat is currently in their possession. However, the microchip is registered to my fiancée, and we have text messages where they acknowledge that the original plan was for the cat to stay with us permanently.

There are veterinary records under multiple people’s names because everyone was involved in caring for the cat while we lived together.

Given these facts, what legal options, if any, would we have to establish ownership or recover the cat? How much weight would a microchip registration and text messages acknowledging the agreement typically carry compared to the fact that they currently have possession of the cat?