Images and Cover Image getting mixed up

Help! I’m having a new issue where my cover image and post images are getting mixed up. I try to post a cover image and it disappears or ends up within the post when I try to add post images. It’s a simple blog website I’ve had for years and I’m seriously considering abandoning WordPress all together when it’s one issue after the next. Any guidance would be greatly appreciated!

The page I need help with: [log in to see the link]