Based on a book I haven’t read and didn’t know anything about before seeing the movie. So I don’t know how much is true.
But it creeped me out. Forty-five year old Charles Dickens falling for someone when she was not yet eighteen.
Yes, I know I’m looking at it from my modern point of view and things were different back then. But still. It creeped me out.
If it was supposed to inspire tender emotions, it failed. All I saw was a man losing his mind, throwing away his sense, and forfeiting his dignity.
But many men do that, even today.
Mike Cane’s xBlog 
I haven’t seen the movie but I have read Drood (http://en.wikipedia.org/wiki/Drood_(novel)), which is quite good. Interesting note: Loo Brealey, who plays Molly Hooper in Sherlock, played Ellen Ternan in “Little Nell”, a play by Simon Gray (http://en.wikipedia.org/wiki/Simon_Gray).
As per Twitter: I should have added originally that he was being disloyal to his loyal wife.