I have a couple of different thoughts on this, some might not apply after you have explained what hurts you about the email, but I might not have time later so putting this down now.

1) my T always says that even though you have a special, paid, whatever relationship with your therapist, you still have a relationship. Some things a T might change, say for example he did that with the stone for you, right? At first he was uncomfortable, then you two discussed it, eventually he was okay with it, and now he's fine with it, if you want a new one or keep the old one and so on. But that doesn't mean he has to change everything you so feel comfortable, which I also think you agree with, as far as I remember from other posts.
This seems to be one thing (and even though he doesn't explain why, at least the 'standing up' thing is something that I'd consider a 'minor' thing if people did that with me) he's not willing to change. People do that in relationships, I might change the fact that I put up flowers everywhere if my partner is allergic to flowers, but I might not want to change every bit of how I like to decorate.
The way this is normally resolved between me and my T (as well as with other people) is by talking through it. If somebody just goes along with everything that you want, this will not help you or be good for you.

I feel like your T felt that he should respond to you early, at least I'd have felt that way if received your email. And since you said you'd be fine with a longer response, he might have wanted to explain a bit (which as he said in his response, it's easy to understand the same text sooo many different ways).

2) This might sound harsh, which I really don't intend. This is just what I keep thinking when reading your posts (though I don't have enough time anymore to post as much, I still read this forum very frequently).
You said that part of it might have been that you saw what R was like, could distinguish between what was missing in your relationship and what you might also like better. I think this is part of why I'm not a big fan of having two therapists or seeing a backup therapist every time a T is gone.
A backup T is fine in certain cases, say my anxiety once sky rocketed like a day after the start of my Ts vacation (unrelated to him) and I didn't have anyone to turn to. But to see them 'whenever' your T is out of town, that just makes things much more complicated, confusing and hard. You might see things that you like better about somebody else, and then constantly search for that in your T. Similar to having a partner, but at the same time seeing what all the other people seem be be more suitable at. 'The grass is greener on the other side'. Sometimes it can be beneficial, like to talk your through a immediate crisis, like somebody died, you suddenly start to have hallucinations, whatever. But just doing regular therapy with them is something different, different Ts have different styles, different approaches, it can interfere (just like two medical treatments for a physical disease can).