I think there are two options for plot in this episode, but both of them revolve around Belle learning that Rumple is the Dark One again.
1) Belle learns Rumple is the Dark One and decides that she loves him no matter what, flaws, darkness, deception and all and the reunite in the Underworld. Belle also tells Rumple she’s pregnant and Rumple suddenly has even more reason to survive the Underworld, while having some sort of change of heart that he really *does* want to be free of the Darkness. “Her Handsome Hero” is a reference to Rumple, unironically, and Rumbelle enter safe water.
2)Belle learns Rumple is the Dark One again and decides she’s absolutely had enough. She’s tired of the lies, the deception, the darkness, and the back and forth. She tells Rumple she’s pregnant but that he cannot have any part of/limited contact with her or their child’s life. “Her Handsome Hero” is still a reference to Rumple but ironically as Belle breaks the S.S. Rumbelle for the rest of the season/series.
No matter which situation, at some point, we’ll see Belle in the flashback reading aloud from “Her Handsome Hero.” The line will be the overall theme to the episode and will reflect on Rumbelle, either unironically (version 1) or ironically (version 2). Look for Belle to spout the line in the present day to Rumple in the Underworld, again either unironically (version 1) or ironically (version 2).