In this case, she totally had it coming, I'm afraid. I would say give the man community service and counseling to help him cope with what he did, and that's that. Sorry, I don't condone cheating, or public humiliation. This is coming from a married man, as well. In this scenario, she probably ruined this guys life.
Edit: Not condoning murder, murder should never be an answer, but we are talking hypotheticals here.
Edit: Not condoning murder, murder should never be an answer, but we are talking hypotheticals here.