Could someone give me some advice?

Ask the second girl out; the one you're infatuated with. You may find out that you like her more than the first. We always feel we want the one we can't have. See if this is the case. It may also be that when the 'first' girl sees you're interested in someone else, she may suddenly realize she could be losing a good thing. At least give it a try. Good luck! :)