Fridge Logic: Why didn't Henry court Abby in the normal fashion and suggest moving back to the island later? OK, it wouldn't have been perfect and there would still be the issue of Wakefield for Henry to deal with, but she wouldn't have found out their relationship and it would have a much higher chance of success.
It's still unclear why Sheriff Mills never knew that his wife had a son with Wakefield. Surely during his arrest and prosecution for attempted murder of a police officer way back in the past, Wakefield would have mentioned it as an explanation of his actions.
Furthermore, what was the point of Henry even staging the wedding to get Abby to the Island? Not only does it make no sense to go through the whole charade of finding a woman, entering into a relationship with her, getting engaged and planning a wedding, when the woman he really wants is Abby, but his entire plan all hinged on her actually accepting the invitation. How screwed would he have been if she had said no?
Fridge Brilliance: Wakefield's philosophy is "kill the ones you love". He kills Sarah Mills for this reason but, in organising the 2008 rampage, he is also partly responsible for the death of the other person he loves: his son, Henry.