Dyson, you are not committed to either girl. Going to dinner with one does not constitute the cementing of a relationship, or the promise of one thereof, or even the potential of a promise thereof. In my former job I happened to run into an old college friend of mine, always fancied her but at this time I have the girlfriend I have now, asked her for a drink and we did. Catched up on what had happened to us over the past 5ish years, no strings attached.
From what you've been saying with this Newcastle girl, nothing is official. As such you are still a free man.
I say go to dinner with this lass.
Like that stops them, they have a shit load of strap-ons.
The only true lesbians are the ones whos dress like butch men.