Lisa, you create your characters, yeah sometime a character likes to take control but it still doesn't change the fact you created him/her and have ultimate say.
Just come up with logical answers:
What kind of person is Nick before and after said ex?
Why does Nick having an ex girlfriend move the story forward?
What could the ex have done to him that changes him or something... that again moves the plot farther?
If as you said she left him for a nice guy. Was Nick not a nice guy? Why? Does he now want to be? If so is it because he really likes Hannah and wants to keep her?
What moves the story or character forward is the big question.
I had a mini problem when i first created Jake, what did his ex girlfriend Susie do to him? Answer i decided on? She used him. Why? Because that is his final epic realization when she comes back, she is still only using him, and that's why he eventually falls for Andy because he knows she never has, but then freaks out when he finally kisses her and she pushes him away, because then he suddenly thinks she was just using him to have someone to talk to and be her friend, meanwhile also leading him on.
Just come up with logical answers:
What kind of person is Nick before and after said ex?
Why does Nick having an ex girlfriend move the story forward?
What could the ex have done to him that changes him or something... that again moves the plot farther?
If as you said she left him for a nice guy. Was Nick not a nice guy? Why? Does he now want to be? If so is it because he really likes Hannah and wants to keep her?
What moves the story or character forward is the big question.
I had a mini problem when i first created Jake, what did his ex girlfriend Susie do to him? Answer i decided on? She used him. Why? Because that is his final epic realization when she comes back, she is still only using him, and that's why he eventually falls for Andy because he knows she never has, but then freaks out when he finally kisses her and she pushes him away, because then he suddenly thinks she was just using him to have someone to talk to and be her friend, meanwhile also leading him on.