Well, Amber.... I hope you can withdraw with love from Hol's process.... but maybe shine a little light on what appears to be a pattern for her in relationships?
One of my girls has labeled it a "daddy issue" and SEES it for herself, and in her last relationship, which apparently she's still tethered to by internet... in case he changes. In other words, it's over, BUT if he manages to make huge change (unlikely) she'd date him again.
It looks like dd hasn't finished all the lessons there yet. I'm amazed and happy she's SEEING it as childhood trauma issues popping up... needing work.... getting attention. She has distance on it I never had at that age, for sure.
From here..... I so want to tell Hol to consider looking over her history..... asking her if it has any meanting THEN telling her to let you know how things work out for her....and drop it. Go back to what you've been doing.... editing, curating and considering what a comfortable life, for yourself and B, will look and feel like. On the feet. On the eyes... the way you feel when you occupy your space.
I noticed you shift from Hol BACK to yourself, B and your space... to the future... to B's ongoing struggle with the healthcare system and perhaps legal battles, and whatever comes next for him and his health.
I also think it's time you put a deadline for being OUT of your house and IN the hut, for Hol and the boy. Your post felt like Hol is determining that, stretching out the date, for whatever reason.... her comfort, perhaps. I don't think she needs more comfort... as you said...you're done being her sounding board to enable her to keep repeating mistakes and stay in untenable situations.
Maybe shifting her INTO the hut, sooner than later, will help her shift out of her old habits.... just squeaking by and hanging on to something that's not going to work, OR needs a strong kick in the rear to improve, or not improve.
I'm all about economy of motion, and you have a house to prepare for the new life you're launching.
It's difficult for me to imagine you putting up with the boy's ongoing messiness, and Ho's stuff all over the place..... even for one minute longer than necessary. HOL can put up with her stuff all over her place, and the boy's mess , without involving you. Why should you suffer too?
Something to think about, and it doesn't have to be delivered with drama... it can be a very calm boundary. It can be a very good lesson on HOW to be assertive AND kind, but firm.
I have the feeling Hol will deploy these very useful tools for herself.
Lighter