This is such an unattractive quality in your bf (and yes, I have read all your updates). He's a 30yr old man, and should 100% have been appropriate, decisive, put his foot down, stuck with it and not involved you or anyone else. He had fed into the drama.
– He should damn well know it's beyond inappropriate for his ex to spend the weekend with him
– He should damn well know it's beyond inappropriate for his ex to make demands that you not be around
That should have been his first cue to say 'Sorry, my place won't be available to stay at. Hope you find an alternative' – not babysit the situation by ringing around and finding her accommodation. If anything, that's his sister's job as the host of her wedding guests. But really it's the ex's job, full stop.
But what did he do? Send you screenshots, went in loops about it, updated you as to her feelings and his sister's feelings, bobbed around feeling 'stressed and uncomfortable'.
To the long, whinging message she sent him, the only appropriate response to that should have been 'I won't tolerate this kind of conversation about my partner – it's best we don't communicate again. I wish you well.' And blocked her.
But no, he sends you screenshots again, wringing his hands about the effect it's had on you. The only effect that could have been controlled is how he chose to handle it, and he failed.
Good luck with a 'man' like that.