Before I come I normally feel or fantasize about my girlfriend’s feet. Is something wrong?

A preference for a particular body part is completely normal. You have for instance breast guys, leg guys and ass guys. Feet are normally not on top of the list, but you are definitely not the only one who loves these extremities. Some girls and guys hate it when they discover their preference is exceptional. But you can also consider it a nice way to get excited. So enjoy it. However, be careful it does not become the only way to get excited. For then it’s no longer a magic charm, but a limitation.