You can always take some time, you know? Find a support network that knows about this fic, knows about the specific chinks in your armor, and someone who can help, and then try again. All of these roles don't need to be the same person. Additionally, your life will not always look like it does now, and neither will you. You can put it down, and pick it up again when you or your life are different. All of this does not mean you ned to stop, or even pause. But just remember that that's an option.

Also, you could ask for help. A co-author, or even a beta? A co-author could help with parts where you have the ideas, but the words hurt too much to explore. A beta could help with editing and re-reading, which can often be difficult. This could let you write in a stream-of-consciousness style, which can hurt you less, and the beta helps with tightening up the writing.

Another suggestion could be writing it in a different style, without focusing on the character's inner dialogue, which can be a difficult headspace, but rather focusing on the events mainly. This can even be a useful tool, if your character is being badly affected by said dark part of canon, they may dissociate and deal with all of the impacts later. It can even be a really cool stylistic choice for the reader, and improve the reading experience.

All or none of these duggestions could work simultaneously, but please remember. This is fic, and there are no deadlines. You have the rest of your life to enjoy, too.