...Quite honestly this would be much more moving without the romance between the two of them. Dating yer parent's old flame is, regardless of the circumstances, just a wee bit questionable...
Well, the author does a good job of selling the emotions and events behind it that would lead to such a striking choice, I suppose. But also, realistically, this doesn't seem likely to be a very healthy relationship, either, despite it being depicted as a healing experience. That's just way too much baggage they're going into things with... :/