When you want to stop, say so once, in plain words, and then stop writing. "I do not want to continue" is a complete message. You do not owe a review of what was good, a list of what they did wrong, or a meeting to explain it. A second conversation is how an ending becomes an argument.
Do not meet them to say it. A public coffee to "talk properly" is still a meeting, and it is harder to leave than a message. If you are worried about how they will take it, that is a reason to stay on Only Amour, not a reason to see them again.
Do not threaten to tell anyone. Their spouse, their workplace, their friends. Discretion was the arrangement. Ending it does not release you from that. A threat is not a boundary. It is the thing that turns a private ending into a harm, and it is a reason for them to report you.
Delete what you promised not to keep. Photos, a surname, a workplace, an address. You cannot delete what is already on their phone. You can stop adding to it, and you can remove what is on yours. Do not save a copy "in case".
If they keep writing, use Block. They cannot message you on Only Amour, and you cannot message them. You do not owe a warning, and you do not owe a reply to the next note. The guide on how to block and report someone is where the buttons are. Report them if the messages become threatening. Say what they sent. Do not attach the photos.
Afterwards, leave it. Do not reopen the thread next week with a softer version, and do not look them up somewhere else to check they are all right. An ending that stays ended is the discreet one.
Create a free account to message someone on Only Amour.