Hi, welcome to PPG!
(I'm not a huge expert on IWD, but I believe the only way to get proper HoW dialogue would be talking to the guy in Kuldahar and agreeing to his proposal - just the way you've done, so you're fine, you haven't done anything wrong).
I see the problem: you've probably thought that HoW romance should follow IWD romance, just like ToB romance follows SoA romance. Alas, the game is not built this way - the game revolves around IWD campaign, and HoW is just a huge extra quest that can be taken any time after Chapter 1 begins. I usually recommend people to play HoW sometime after Chapter 3 - Chapter 4 and 5 are fine, too, but the final chapter of IWD is the story's finale, when the romance comes to the *final* part, so the Easthaven crystal is supposed to be an ending, yes, and HoW may be a let-down after.
In HoW, you get your regular NPC-NPC banter, two friendly/character talks with you for each NPC. For your romance interest(interests), you get two player-initiated lovetalks for HoW and one for TotL, BUT you only get the HoW talks and the TotL talks with Nella(or Teri, or Korin/Holvir for girls) if you are still in "continued" romance, i.e. not if your romance/match variable is at 2(the final stage) - because stage 2 is the ending of Chapter 6, when you are teleported back to Easthaven, and you can't continue to HoW from that - your story's over.
I AM really sorry for the inconvenience - I will put it loud and clear in the readme, for first-time IWD players especially, that I recommend to play HoW with your romance interest before the final stage /chapters of the game.