In the beginning of my relationship, me and my girl were both insecure about ourselves and we were both pain in the ass about this kind of stuff to each other. Wanted the other one to change but didn't want to make the change ourselves. We would argue with each other about the other one looking at X person at the store, Y person came up to you and you didn't tell them to go away, etc.
Honestly, I feel like the jealousy went away when we both stopped consuming pornography. It's not forbidden, but neither of us really watch it. There was a lot of other factors obviously, such as communication and living together made things easier. I just think when you view sex as something not intimate between two lovers, then it makes sense why you would think your partner views it the same way. Obviously this only works if you both have the same view about it, though.
I think it's possible for this to happen in a relationship, but it's probably very rare.