Your heroine has agreed to help your hero’s ex (wife, fiance, girlfriend, you decide). Your heroine has mixed feelings about helping her.
Jealousy and distrust are definitely an issue but your heroine is also the type of person who feels compelled to help people when they are down, regardless of who they are.
What does your heroine do for a living and how is she helping your hero’s ex?
What does your hero think about this decision and what role does he play in your story?
For example, does he work with your heroine and now he’s obligated to help as well?
Keep in mind that this type of storyline can be timeless and it can take place in any world. This could be anything from historical to urban fantasy or even erotic romance. Have fun with it