Not an expert in these matters. but here are my 2 sats..

Allow yourself to feel what you are feeling.

Don't put that Ideal Noerms and weigh your present against that ideal guy.

Also, it might help to acknowledge this (without any accusations) to the other person concerned, your GF in this case.

This may or may not change any of the behaviors but at least you will feel free mentally.

This feeling can come in non-romantic context too. How would you tell your mom if she was too protective of the next-door kid and you were jealous of them?