Yes, it will hopefully be a step toward 'sorting things out', and the end of things as they are. Which is surely what you want? It's cruel to yourself to go on as you (collectively) have with a plain lack of honesty and a deception over recent times. THAT is not a healthy relationship to be having. Would you actively choose to live like that?
'Finishing things' is not the end of the world by any means. You can be fearful of it, yes, as it is a potentially scary prospect and it means unbidden changes, BUT it brings opportunities too, and people often forget that in their sorrows. Ideally he should be out of the house prior to counselling - is there any movement there? I ask as your concerns about him just dragging stuff out with absolutely no cost to himself whatsoever remain, and become more evident. From what you say so far, his life hasn't altered one iota whilst yours is being compromised. The cruel selfishness continues.
DF - did he call? You have no way of knowing what he may say. Perhaps he has spoken to his partner and she has replied "You said WHAT?? You eejit."
Those books? Why are you reading them, and putting further pressure on yourself? (obv with no idea what they are.) You demonstrate a firm grasp of what is happening and how you feel about things and what your decisions should be, and for me I'd be dubious about the value-added of stacking up on books. You have all the necessary tools at your disposal already. Using them is where there is a hold up, I'd suggest. Again, rely on your own resources and resilience. Make your decisions and stick to them.
I'm not sure about the 4/5 people. As anyone would say, focus on the benefit of the other 4. Place the 5th one in a mental drawer labelled " Unexplained phenomenon which may become clearer over time." That would otherwise pointlessly drain you.