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The writer is so blase about her menage a trois. She gives no indication that she wouldn't do something similar in the future. It sounds like she has no superego on sexual matters at all, and she says her boyfriend should get therapy and get over it.
Her boyfriend sounds like someone who had some moral upbringing (apparently an increasingly rare situation).
What really is bizarre to me (a 69 year old male) is the number of responders who agree with the writer.