Messenger pics iv sent to friends move sometimes to gallery Samsung Tab 4. Pics I send to friends on messenger (facebook) have started showing up in my gallery under messenger app , but only sometimes.Even ones I delete show up there sometimes . My second problem is stuff under messenger ,screensshots and Facebook apps in my gallery vanish . Please explain in easy terms if anyone got any idea as I don't know all the jargon yet . THANKS .
On Facebook Messenger,

Go to Settings › Photos and Media.

There uncheck the two options, if you wish to. This will stop messenger photos from appearing in the gallery in the future.

My Messenger is version 55. I think this option exists in all recent versions, too.