I decided on Hexxer.
Oh god they have so many curses.
Several ways to build a Hexer.
Since you have a DH already, I recommend you don't go full bind build with your Hexer, assuming your DH is using whips. Kind of a waste *at this point of the game*. Right now you will probably benefit more from having ailment options than from having more binding. However it might be prudent to get 1 bind skill so you can attempt to apply more than 1 bind in a single turn.
Revenge is
broken amazing in EO2 but not really that great in the Untolds by comparison. However it's the only real damage spell you get in EOU1 so consider it long-term. It can be good in a pinch but you can't really build your party around abusing Revenge in this game like you could in EO2.
Frailty Curse is must-have. Sapping is useful as well. Torpor is also must-have. Evil Eye with at least 1 of either Muting, Conflict, or Suicide Word is also must-have. Conflict is the best general-purpose of the three. This is all for any build, really.
Stoning curse is also very useful as a OHKO spell but it is TP-intensive. Still worth it for the leveling/exploring phase of the game. Also some conditional drops require killing via petrification and it's more reliable than enemy skill grimoire stones.
Rinko's (my hexer) build at endgame was
Curse Mastery 10
Sapping 10
Frailty 10
Leaden 5
Deceit 5
Revenge 10
Blinding 5
Madness 5
Torpor 10
Cranial 10
Abdomen 10
Immobile 10
Evil Eye 10
Conflict Word 10
Grimoire
Spark 10
HP Up 10
TP Up 10
Dilution 10
Stoning Curse 10
Gun Mastery 10 [unless I'm fighting a boss she uses a gun for better basic attacks]
Recharge 10
For now, though, since you only have a third of that amount of SP to spend, I would prioritize maybe something like Frailty, Torpor, and Evil Eye, then spend some points on other things as you see fit.
Be sure to equip LUK boosting items. Bind and ailment success is based on LUK stat.
How do I make a hexxer work well with a sword dark hunter?
You get Blinding Curse, Corrupt Curse, Evil Eye, and Relapse Curse for starters. Basically you want to get ailment options your DH doesn't already have, and then have Relapse to make sure your DH has time to use Soul Liberator on ailing enemies before they recover from the ailments.