You can't 'upgrade' your girlfriend. This new girl isn't "better" she's just new, and that makes her novel. There are lots of things you'd get to re-experience with her that you aren't getting in your current relationship.

It may well be that you could hook up with New Girl. But getting out of a relationship, one that you say is 2+ years old, takes time. You don't want to be the kind of person that can throw one relationship out the window and hop into the next one without a second thought.

You are probably more at fault for your current relationship's state than you say, though you may know that. I'm not judging. But unless you're just looking for tail, you probably aren't going to be in a good place with either person for a good long while. If you break things off, you'll need to clear your head; if you try to patch things up, you have to let New Girl go.

You could be onto something. While >>3423 has a point that you don't want to just throw a relationship away, you may be at a point where your current relationship is junk, but you are still clinging to it because it's familiar. Ask yourself if you are just going through the motions with the missus because she's what you are comfortable with. In other words, is this a relationship of convenience?

I'm not saying you should rush headlong into a breakup. The grass may not be greener on the other side. This customer may not even be interested in you; she may just have a flirty personality. But she was the catalyst that got you thinking "Am I content with my current relationship?" If you can truthfully answer that question in a vacuum, without dreaming that better options are out there, you will have made a great step toward solving your dilemma.