Does it have to be quitting or saying goodbye? Perhaps it's just that you're at a point where you can stop seeing your T right now - that doesn't have to mean forever, unless you want it to. You could talk to your T about spacing appointments out to once a month and see how that goes, or even just plan a short phone check in. If all is still going well, you could wrap up for now with the understanding that your T is available, should you need her again.