I agree completely; I find it very difficult to choose someone else.
In Pattaya last month I had a massage with an old "friend" who now works at Scandic Massage. But the next day I caught up with my regular guy and spent the rest of my holiday with him.
I felt guilty for abandoning my massage guy so I had to work out a strategy to enter and leave the Ambiance Hotel unnoticed. It was quite a pain.
One night I needed to go to a convenience store around 2am, but rather than walk to the one on the corner - 30 seconds away - I had to sneak out the hotel and go to the one on Beach Road. And in the rain!
Telling the guys you are a butterfly is the best way to get around this problem. I'll be in Chiang Mai next month and will be spending every night at Adams Apple. As in the past, that's exactly what I'll be saying to them. As they know in advance that I'll probably be taking different guys there shouldn't be a problem.
I agree with Oceans - the guys are used to hearing "No" so we need not worry too much. But I can't help it and have missed out on some fun over the years because of my attitude.