I'm way over invested too. Their marriage only just survived Ross' infidelity (if that's what you call it) but could it really survive Demelza's? Taking into account Ross' character, the time that this is set in and the position of women in those days, I very much doubt that Ross would be so forgiving. As an outsider we can see it as an understandable 'wobble' but I doubt very much Ross would see it that way.
I also hate the way Ross spoke to Elizabeth at the graveyard. He as much as said that it was her fault that he raped her! I still love him though <shallow>