A woman should as much as possible to think about it: constantly jealous, "wind the" myself only weak, insecure people who fear that they had neither the strength nor the charisma to keep a loved one. In other words, if a girl is constantly jealous, she thus "signs" that it is stupid, neobayatelny, non-sexual. It is very strong, convincing argument. Not what a girl wants to consider themselves such.
But we must not and hit the other extreme, that is suspected to suffer and suffer in silence. The best way - to speak frankly with her boyfriend in a suitable environment. Calmly, without reproaches and tears, without scandals and tantrums. We must speak clearly, but essentially without losing on unnecessary items, do not "beating about the bush" (alas, the fair sex often suffers from it). Briefly and clearly explain to the guy that just did not like that led me to suspect. And be sure to emphasize that if he may be dear to her, she never would start the conversation! That's because she loves him, she did not want their relationship marred suspicion and innuendo.
As a rule, the guy in this situation adequately react to the revelations of the girls, that is, give her a plausible explanation and assured that her suspicions are groundless. In this case, it should calm down and no longer torment jealousy neither himself nor his. If it continues unabated overcome this destructive feeling, then there are only two ways out: hard "work on yourself", if necessary by resorting to the help of a qualified psychologist, or be prepared for the fact that relations will sooner or later come to an end. Exhausted and angry morbid jealousy guy just go away. And the blame for this will only revnivitsa.