Lucy and William have an unbreakable bond based upon all they have been through together, and the fact that they have two daughters. They are comfortable around each other with no need for pretense and that is refreshing. They have genuine affection for each other, and care deeply for one another.
William is a fixer, and he knew that Lucy did not understand the scientific aspect of the pandemic, so he wanted to take care of her & keep her safe. Selfishly, though, he didn't want to be alone and I agreed with the daughters' questioning whether he manipulated Lucy into going to Maine. I think spending time in Maine with him during COVID was a healthy choice for Lucy -- physically and mentally -- because she would have been a wreck in NYC during those days. But it also served William's purposes.
However, I was disappointed when they decided to stay together in Maine for the foreseeable future. Lucy is settling for less than she deserves by staying with William. Yes, she feels safe, but safe often translates to stagnant. She is staying with a man because it is comfortable and familiar to do so, and mssing out out on the possibility that she could find another man who would adore her the way David did. And now William has surgically been rendered impotent? Does he really love and cherish Lucy, or is he just selfishly using her so that he won't have to spend his final days alone? I suspect that's the truth of it, and Lucy is simply going along because she is also afraid to get out and bravely seek out a fulfilling future for herself. It's a disappointing outcome, in my opinion, but a believable portrayal of a truly codependent and, in many ways, dysfunctional relationship.