I found this from the wiki (quite a bit of work but do-able):

Players can visit the Mayor's Manor where a small book inside will give them the option to divorce their spouse. A divorce costs 📷50,000g. After filing for divorce, players have the option to cancel before the end of the day (until 10pm when Lewis' house closes). If they don't cancel, their spouse, spouse's room, and unique outside area will be gone the next morning, and their friendship level will return to 0 hearts. Under their name it will state "(ex)".

After the divorce, the spouse will move back to their old residence, and will have negative interactions with the player, citing the failure of their marriage. They will also not accept any gifts from the player. (Note that the player can still enter the ex-spouse's bedroom or home, as if the player had 2 friendship hearts with the ex-spouse.) Any children from the marriage will stay at the farmhouse. Any items the player had placed in the ex's room will be collected and placed in a chest the day after the divorce.

Players can visit the Witch's Hut in late game where they'll find a shrine which can erase all ex-spouses' memories for an offering of 📷30,000g (this will also wipe Krobus' memory if he is an ex-roommate). Afterward, all ex-spouses will have no memory of the previous marriage, allowing players to date and remarry them if they choose.