Google "PEA". It's all about the brain chemicals. The only thing that will END it, is total withdrawal from the source of the high. Complete no-contact, and SHARP withdrawal will take 3-4 weeks, and she won't be completely over him for about 4-6 months. And ANY contact will re-set the clock to 0:00.
My wife's most outlandish comment was, when told by her father that her mother had been sobbing all day over her daughter's affair, said "Well, tell her that she needs to get over it."