Why is my wallpaper showing up on my partner's login?

Me and my partner has 2 different logins and everytime I change my wallpaper it shows up on his screen messing his wallpaper up. How can I get that to stop?

if you both have your own logins you shouldn't be having this problem.right click mouse on your desktop making sure you don't click on any icons just an empty space on desktop then click on properties then click on the tab desktop and pick your wallpaper and tell your partner to do the same when you've finished and see if that works if not then I'm sorry I can't help you.goodluck claire87.