I've started fantasizing about my ex girlfriend after moving in with my new girlfriend.
Why are you still hung up on your ex?
I've been researching her online and she actually seems really great, no wonder I fell for her.
You're with your new girlfriend now and fantasizing about your ex makes you emotionally unavailable to her. Try to put your ex out of your mind.
It's fine, my girlfriend doesn't mind if I think about other women.
I think that some degree it bothers her. You should do what you can to become more emotionally available to the girl that you are with.