I can't keep up with this thread so am only skim reading, but I have kept coming across stuff about whether there was an argument and also whether OP would argue without his prosthetics on.
I just want to say that not all arguments are conducted at top volume, standing up and throwing things. I think OP's texts are suggestive of someone who was possessive and controlling and it sounds as if his behaviour could be emotionally abusive. (this is my opinion - I know there were loving texts, but then there would be - that would be a common feature of abusive relationships especially at an early stage.)
I know of one person, who was extremely controlling with his wife (they are now divorced) and he used to bully her and go on at her verbally for hours - one time even on a car journey with the kids in the back. But he managed to do this in a low voice without the children being aware. We have stayed in the same house with this couple and she has told me since that they were up until 3am arguing but we didn't hear anything.
So this is speculation but I can quite feasibly imagine a scenario where they were lying in or on the bed talking (in which case he might well not have had his prosthetics on for comfort), which turned into an argument because of something he didn't like about her lifestyle, friends etc and this led to her having enough and jumping up and saying she was leaving. It's even possible she stormed out to the bathroom to avoid continuing the argument.