Hi there Hitchcock and welcome to the forum!
Your post displays a lot of thought and well worded descriptions of the situation you are in.
Something needs to be changed as you will probably agree it cannot go on like this with you gradually spiralling downwards amongst the tension.
I have been in a similar situation! A natural extrovert (chatterbox according to my wife), it feels very strange to not chat when with someone - about almost anything! Yet if I make and effort to talk less, I get asked what's wrong! So I asked my group friends one day if my chat really annoyed them. Their reply was instant - NO WAY - don't stop, keep on exactly the way you are! We all had a good laugh and sometimes refer to that occasion today when together - the point is it cleared the air and made me feel much more relaxed about my relationship with the group.
As humans, we all have our own set of values and personality pillars - these must be honoured and followed otherwise we cannot function properly and reach our potential. In your situation, it sounds like you just cannot be yourself which is not healthy.
I wonder how Sarah would react if you asked her to have a chat evening about your relationship with her? Think carefully about it beforehand, and be careful to not criticise her. The angle might be that you know you love to chat all the time, even to the extent that you find your own chat annoying from time! You have noticed she doesn't respond much, and you just want to understand if things are OK between the two of you. Are there any things you do that might annoy her? What does she feel about having you in the house? Would she prefer you to talk less?
As you can see, the list can go on. What's more important its that you prepare beforehand, do not criticise her in any way (otherwise she will get defensive and not give an open response), and really listen to what she has to say.
As with the outcome from own situation above, I am picking that she will respond in a way that clarifies things, even if not as positively as you would like. At least you should know what's going on and can decide what to do based on that information.
This will take some courage so good luck with it - very happy to discuss further if you want to!
Regards, The Bro