someone on another site suggested something very interesting about Louisa/s motivations for leaving, which at first I pooh-poohed and then I thought about some more. (I am not naming this person b/c of privacy, however, they should feel free to come forward and take credit!)
So, the theory was, suppose Louisa was unhappy and felt she had to leave b/c she believed Martin didn't love her anymore. That made her unhappy, and her assumption about his unhappiness is that it is because of her. Are we seeing the priest/pig farmer's warning playing out Can I make him happy? No, it seems not, and that makes me miserable.
There are several bits that added together make me wonder if there isn't something to this theory. First, there's her very evident disappointment when he blew off the "two week anniversary." Then there was the "but I'm your wife" line, which I thought was delivered with some hurt and disappointment. Finally, the scene where she asks him if his problems are "because of me" and is not convinced by his answer. He's not confided in her, or responded to her, and probably, if he's as depressed as he seems, been privately (i.e. bedroom) affectionate either.
Now, not saying all those bits are entirely convincing --- but I wonder if they weren't meant to be? We know, or we think we know that she's pretty insecure; it would be no wonder if she attributed his current state to something she did, or tofalling out of love with her -- not looking beyond it more generally to what could be the matter. And, we remember, that she only agreed to come back to him in S5, when he was able to express his love to her.
We, the audience, know that she couldn't be more wrong. So now, we (or most of us, certainly not all) want to shout at him, go after her, man! Try to tell her that what's wrong has nothing to do with her and in fact is infinitely worse by her leaving and taking James, that in fact he needs her. As he does.
I doubt it will play out quite that romantically, but I'd love to see it.