Good guy vs Bad guy

The good guy in my novel "Teaching Tori" is Tom. He is pretty perceptive and doesn't take long to notice what is going on with Tori. He has a distinct sense of what's right and wrong, and hates that Tori won't accept his help.
Tom can be pretty tough, too. Once you've lost his respect, you are most likely never going to win it back, no matter how hard you try, or how sorry you are. He might forgive you, but he won't forget.

The bad guy is Gerard. He is sneaky in his ways to undermine Tori. He belittles and puts her down in front of her colleagues. He isn't interested in her opinion.
In short, he is a rather unpleasant person.
The problem is, he is the principal of a small school. So he needs to have some redeeming features. It is unlikely he would have ever been selected for this job if there is nothing positive about him.

So I'm trying to find the good in him:
  • He loves his granddaughter to bits. 
  • He likes to be seen as a fatherly figure who is taking charge of his disciples. 
  • His school is neat and tidy.
Are these characteristics redeeming enough? I don't think so.
So what other reasons could there be for his attitude towards Tori? I thought about some possible reasons:

  • He has gone through some sort of trauma or grief. Maybe Tori reminds him of a daughter who got killed in an accident?
  • He feels threatened by her because she is young, confident, attractive and a woman.
  • He knows that she doesn't really respect him on a professional level. He doesn't meet her high expectations of a school leader, and she is not too afraid to let him know this openly. He can't handle that he feels like a failure in her eyes.

My challenge is to get Gerard's point of view across when my writing is written from Tom's or Tori's POV.
I've tried dialogue. A short argument that reveals the origin of Gerard's and Tori's dysfunctional working relationship.
I'm just not convinced that it is enough. He comes across as so one-sided that he's not quite believable.

Have you ever had the problem that your character was inherently unpleasant, despite your efforts to make him/her more balanced? How did you overcome this?