Minnesota
Nice that special connections can be made in the hobby! Here's to 25 more for you. 
Having an ATF doesn't mean you can't see other providers, for the variety you seek. But it would mean seeing her more than twice!
I think for an ATF relationship to work, both parties need to invest in making it work. Obviously the provider has to understand that just because the guy is a "regular', she can't take him for granted and slack off on her efforts. But the client needs to do his part to make each visit special too.
The other thing about an ATF relationship, I think, is that it goes beyond just the sex. If you're going to spend many enjoyable hours with a woman, and she with you, you both need to enjoy each other's company in ways other than sex. In other words, there's that "connection" that we read about so often in reviews. If the "connection" isn't there, there's not much hope of a good ATF relationship. Usually by no later than the end of the 2nd date, I know if there's a "connection" or not. A few times I knew after the first date, or even in one case a few minutes into the first date, that there was ATF potential.
I realize ATF relationships aren't for everyone. But there's several benefits, for both parties. There's no need for "preliminaries"--you can get right to it if you want. She knows your hot buttons, your likes and dislikes, and you know hers. Because you know each other and trust each other (I think mutual trust is key in an ATF relationship), you feel free to explore things you might not feel comfortable exploring if you've just met. And of course, no need for screening and logistics for each session.
I have never met with any single provider for three separate encounters.
I have always found that the business relationship somehow shifts by the third encounter.
First Meeting: I feel excitement upon meeting and spending time with a new individual.
Second Meeting: The second meeting is -- generally -- remarkable. Second meetings have been among my most memorable encounters. Additionally, second meetings are very important for providers (i.e., it validates their worth due to the number of hobbyists that only visit with them on one occasion).
Third Meeting: I have felt that providers make certain assumptions (i.e., he is a regular and I do not have to make any extra efforts for the session) by the third meeting.
In my experiences, the idiom "third times a charm" does not apply to provider and client relationships.