Honestly though, I would go with the second.
You've already started a relationship with her. There's no point in ending it just because some fling from the past suddenly tells you that she's interested in you. Granted, she's been on a few dates with you which means there is at least some levels of attraction there.
Still, if you already have a good thing going, why stop?
And on the bright side, if it doesn't work out with the new girl, there's always a chance that you can revert back to the relationship with the crush from before. Can't say the same if it were the other way around.
