Are you for real? This is SB you are talking about, not your SO.  That comes with P4P relationships. No strings attached.

That would only lead to hurt feelings. That can be avoided in this realm by just keeping that info to yourself and by finding someone else, right?

So you might want to put this post up there. Just put your cursor on the "TER General Boards" label above left and a list of all the boards will drop down. The Erotic Highway is bottom right.

...that does not mean you need to tell her everything. Unless you think she is likely to up her game, lose weight, tone up, improve her dick skills, etc. with some constructive criticism you can just let her know it's been great and it's time to move on.  

 
If she insists on some reason, tell her the truth, but tell her your truth:

 
"I'm not in a position to sustain my budgeted allowance for you and I wouldn't dare to ask you take less. "  

 
Note: This is true! But here's the same statement before it was carefully edited:  
"I'm not in a position to sustain my budgeted allowance for you (given you poor performance), and I wouldn't dare to ask you take less (because I want to spend my cash on a hotter, more skilled babe)."

 
So you are the kind, gentle guy who is facing the harsh realities of life (mainly her inability to give you wood - now THAT is HARSH!). This is the mature, adult way to let her out of her agreement so she can find a new guy (who may like/pay her more).  

 
Tip: Never let the discussion stray into whether she is (still) worth the allowance. Every SB is "worth" a million dollars! Just ask her! Instead, focus on YOUR budget. She can't argue with your budget because she has no control over it.   And if she actually does offer a 20%, 30%, 50%? reduction, you can decide if she's worth serving as a cheap fuck hole when you are bored or your new #1 SB isn't available.  

 
Please let us know what happens... I think we can all learn from your process and experience.  

 
Life is good

 
The Cat

I see ugly people every day.  Honesty doesn't force me to inform them of that opinion.
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I like variety so getting trapped into seeing just one chick would not be my preference.  I see no need to be cruel about it and put the fault on them.  I'll just have scheduling conflicts or other excuse.  It's not that hard to come up with something that save face for her and gets you out.

I know cuz I'm in a similar situation.  One of my current , longest running (2 years) arrangements is with a girl who was 24 when we met, slim and sexy just the way I like them.  And mad skills in the bedroom!  Now she's 26 and has gained about 40 pounds.  She's still a wonderful girl, I still see her regularly, and she still provides pleasures beyond what most SBs have ever done for me.  But she is no longer a visual treat.  Turns out , that matters to me more than I might have thought.  She's curvy now, "pleasingly plump".  I'd probably never reach out to her if we were to meet for the first time today.  So I'v been asking myself the same questions as the OP.  

Part of the answer is another question:  How many other options do you have?  For me, SA has been disappointing for quite a few months.  I encounter scammers of every stripe, GPS girls, ones that ask for money in advance, and those who make a lunch date but never show up.  So I'm not prepared to end thins with my  chubby SB until I have more in the pipeline.  Once that happy situation develops, I'll have a tougher, more immediate decision to make.