Thank you TER!  I found myself having the delightful experience of double doubles and now I'm really hooked. I can't get enough of this hobby.
Story:
I planned an overnight with my ATF and expected that she would again invite another provider in for several hours for both of us to enjoy.  She had to cancel the overnight, but we rescheduled the day for the afternoon and early evening.  I like at least 5-6 hours every time I hobby.
I was still hot for an overnight, so I contacted the provider who I had hoped would have joined my ATF and I, and arranged to meet at 9 pm.  For some help and added excitement I then invited another provider to join us. I had previously seen each separately and was pretty sure that we would all have an incredible time together.  
The day came and I was on my way to see my ATF when she texted asking if it would be OK if her friend joined us. I quickly replied that of course, I had always wanted to meet her friend.
The first double of the day was absolutely wonderful and I could only leave because I knew what was waiting for me and I was late!
Now I'm thinking of fourples.