In my opinion, it should not matter to the BF whether 1 or 5 million people are in love with his GF, or whether they sit next to her at work or walk down the aisle with her as wedding attendants. It should only matter what the GF does or feels - she cannot control anyone else.
It is not attractive to be jealous for no reason. I really appreciate the stance of my current boyfriend. When I got roses from "a secret admirer" I was worried, based on past relationships, that he would be angry with me, even though I did not know who sent them and certainly did not solicit them. His response? "That's awesome! I am not surprised - if I weren't dating you I'd want to send you flowers too!" This is because his focus is on MY behavior and feelings, not on that of people I cannot control. Here, it seems the GF is living in a state of fear over things she cannot control, such as her past and the feelings of other people.
The BF needs to get over it, and I think the GF should reevaluate her relationship.