Remember how when Molly died Fitz said that he had nothing he could turn to to distract him from the reality of that loss.
When the Fool was gone Fitz immiderly went back to Molly to escape that loss.
Fitz spent the entirey of Fool's Fate unlearning his want for a happy heterosexual ending, and chose the Fool over it. But the dominos from the quarrel had already fallen and the Fool thought that Fitz would truely be happier than him.
And yes, Fitz did want to go back to Molly because of the memories he got back from the girl-on-a-dragon but the feellings he felt from it were very obviously contridictory to his current ones, and whenever he actually thought about it he knew that a) Molly would not want him back, its both too early and too late and b) he chooses the Fool. I think if he got to actually sit with those emotions they would have faded out, and he would not have sought out Molly. We know that because he chose the Fool.
But then the Fool was gone. And so Fitz went to Molly. Doing a huge dissrevice to both of them; not letting either of them grieve burich properly or agknoledge him, ignoring Molly's wishes and using her sons to get to her, etc; and in general acting how he was when he tried to get her to be with him when they were teens *cough cough harrassing*. Repeating the same old mistakes.
He tried to hide that tragedy in the guise of a perfect heteronornative happy ending, but that doesn't work, because he just spent an entire book unlearning it.
He just spent an entire book loving and losing and savagely mourning and choosing the Beloved over that happy ending. So theres this huge dissonance between everything in the Fool's Fate and its ending; So we don't believe him; So deep down, he doesn't believe himself. The comment about not having anything to distract him from Molly's death shows that.
And that "happy ending" he got isn't all that happy. The chapter in Fool's Fate is called "ever after", very clearly missing the "happy". Fitz says he is content. In Fool's Assassin he tells Molly that whenever she is happy he is content. But by the end of Fool's Fate he says he always waits to see the Fool again.
He shuts the wit out, he constantly misses the Fool. He leaves his and Molly's bed at night to write letters to the Fool, which he has no one to send them to.
He refuses any reminders of his life as the bastard prince and as an assassin and a catalyst. Reminders of his life outside his "happy ending" in Withywoods. He refuses to have gaurds. Because if he did have gaurds he would have to egknoledge that he is not Holder Badgerlock. That his life is dangerous. Ironically the very thing he did to keep the illussion of saftey made the place less safe.
There was so much talk of Fitz being (in)complete. Chade told Fitz that people say that children complete a man. And it almost seemed that way when Bee was born. Fitz saw Molly care for her and thought "so this is what a mother is". He tried to build himself what he lacked as a child, the life he could have had had he not been the bastrad prince, had he not been an assassin, had he not been witted, had he not been tortured and used and killed.
But because of that expectation of a perfect life and a perfect child, he did not love bee all her first years as he should have. And because of all those things he lacked, he could not be a good father to her.
He did by her as best as he could, but he simply did not have the tools to care for her. That all became very clear when Molly died. He really did try to do better. He contantly tried but he couldn't just will homself into being a good father, despite how much he loved Bee. And all that doesn't negate how much he loved her, but that doesn't mean she deserved better than what he could do. Despite how smart or mature she was, she still needed what Fitz couldn't do. Couldn't be.
And when his life in Withywoods was gone, Fitz still looked at it with pink-tinted glasses. He still clung to it, to what it represented. But it was not as he saw it. What he clung to it as. So after Bee was taken he felt like past after his death. Because he clung so long so hard to that happy ending. He wanted to die in his and Molly's bed in that "safe", "perfect" life at Withywoods. A life which was never as real as he wanted it to be. Never as happy. Never as whole.