Who is Howard from The Memory Keeper's Daughter and what is their importance?

Howard is a photographer who comes to Norah and David's beach cabin while they are on vacation, supposedly to discuss photography with David. He tells them he is in the process of a divorce. But he is coming on to Norah, and the next day she goes to his house and undresses outside before joining him in his cabin. Norah goes to him ten more times, even though she finds out that he is happily married and expected at home soon. Howard is not necessarily a good man, and he preys on Norah's obvious vulnerability.