The 18-year-old man was depressed after being dumped, and although she unfriended him, he created a second Facebook account to friend her again. The Lancet report said:
The mother was advised to ask him to measure the peak expiratory flow before and after internet login and, indeed, “post-Facebook” values were reduced, with a variability of more than 20%. In collaboration with a psychiatrist, the patient resigned not to login to Facebook any longer and the asthma attacks stopped.Although in this case the service was Facebook, the doctors involved indicated that any social networking site could increase the psychological stress on patients. Of course, in reality the young man was just lovesick, and Facebook is just a new way he could track her post-relationship life.
The temporal relation with onset of symptoms suggests that Facebook login was the trigger of asthma exacerbations, in which hyperventilation might play a key role.5 Other possible environmental and infectious factors were excluded with a thorough history and physical examination.
In other words, instead of needing to go to common friends to see if she was dating other men, he could find out simply by tracking her Facebook updates. Facebook wasn't really the cause, just a tool to exacerbate his lovesick symptoms.