In my opinion, I think Grey is not sure what exactly he feels for you and for the other girl. He wants to meet her to see if he’s still feeling the same way he used to be when he was in New Zealand, whereas he’s developing a feeling for you now.
I understand your confusion, K. But please try to think this way: Whatever (or whoever, in this case) is destined to be yours, it will be yours at last. I think you should let him go to meet this girl and wait patiently. If he is going to be your boyfriend, he will come back to you. Make it clear by asking him that he does choose you. But if not, well, just accept it and move on. I know it sounds easy said than done, but I believe you can go through this tough time and finally get stronger.
Talissa