Gold is suddenly eager to help Emma, Snow, David, Regina, Robin and Henry find Hook so he can return home to Belle; but in order to do so, he must find his ex-wife Milah in the Underworld and ask for her help
Because Milah’s unfinished business is Rumple/Nealfire? So he has to help her move on so he can go home?
This isn’t beyond the realm of possibility. She may regret the way in which she left them aka Letting Rumple think she was going to be gang-raped by a bunch of pirates.