rightwriter,
Regarding what nefarious things you think ubiquitin is thinking, you made it up and it just makes your posts look rude.
Regarding asking someone else to delete the messages you sent them, you have a right to politely ask once, and they have a right to say no. And you have a right to no longer send them personal messages if you think they are not being respectful of your private communications to them. Everything that is sent to someone else electronically should be assumed to be potentially permanently available, and there isn’t much of anything we can do about it. Adjust accordingly.
Did you know that with Signal you can send messages that delete automatically from the recipient’s device after a period of time following the recipient reading it?