I think you might be right that the statement may be too strongly-worded. However, to Heather's credit, she does discount abusive relationship dynamics from this; and to your point, the notion of what is "unforgiveable" within the bounds of a relationship changes drastically depending on the context and the experiences of the individuals involved (excepting, as you noted, where harm or violence are involved). The goal of relationship, if not marriage, is not to find a perfect person -- perfect people don't really exist -- but to find a person or people whose flaws and imperfections fit nicely with our own.