Otherwise, she would be enabling him to commit adultery by marrying or continuing to be with his HS sweetheart.
I think that is a fallacious conclusion.
No one but the person themselves -- who is the one CHOOSING to commit adultery is to blame for their adultery.
No matter what the circumstances -- there is never ANY excuse to commit adultery.
There may be reasons why someone becomes tempted -- but they themselves -- and no one else -- are the reason why they do or do not ACT on their feelings.
I am sure that many people are probably tempted to commit adultery -- but honorable people simply do NOT choose to follow through.
I think that is part of why society is so accepting of it b/c people make all kinds of excuses for people who are adulterers.
Even if Erin or anyone else chooses not to restore their marriage -- the other spouse always has the choice to remain in singleness -- rather than choosing to continue to be or to become an adulterer.
It is always about personal ethics and NOT situational ethics.