I'm not sure I'd say it's "taking you so long" - lockdown started less than six months ago, and you'd been together 8 years.
What is it that you're worried about? Try to break it down into specific problems, then you can start to think about what needs to be done to overcome that.
Is it that you don't think you'll have enough money?
Is it the practical things like sorting out bills, ringing the engineer about the boiler, fixing the flush when it makes a funny noise, checking the tyre pressure (NB before anyone starts, these are all things I have been anxious about, and I still wouldn't know how to do one of them)?
Is it the idea of living without another adult?
Is it the idea of being solely responsible for the toddler?
When you know what the issues are, then you can put steps in place.
From your daughter's point of view, she still has both parents in her life even if they don't live together.
It's possible that your own experience of loss has affected you deeply - it's even possible that one reason you're having such trouble with this breakup (more than you think you ought to have) is because it's brought back the emotions related to your parents' deaths. Perhaps you tucked them away because you couldn't deal with them at the time, and now they're latching on to this.