I don't have a set number.
I keep booking for as long as it feels good, but once she starts taking me for granted - I'm out of there.
I have seen a few ladies who were great for the first few bookings, but after that they started taking me for granted - "Have to leave early to get to the shops before they close", watching the clock a bit more obviously, etc. I'm easy to get on with, but don't try to take me for a ride !
I had a 'regular' who I saw every six weeks or so for over two years. We got very comfortable with each other's needs and just enjoyed the bookings.
Even when she stopped 'working' and got a 'regular' job (her words), she kept on a few old customers (including me) for a bit of 'week end financial top up'. I think there were three of us, but we never met.
I suspect that if we had moved in together we would have been fighting within a few weeks ! (Maybe I should never have married my 'ex' !).
During that time I occasionally saw other ladies when I saw an ad that looked really appealing, but always went back. Then she returned to Sydney to look after her sick mother.