Let's look at this from Seven's perspective.
An Admiral Janeway from the future arrives with technology and knowledge that will allow them to return to the AQ post haste. The captain, however, has a different agenda, and so the two of them, admiral and captain, are in the midst of a disagreement about how they should proceed. All of a sudden, the admiral arrives at Seven's workplace and starts trying to manipulate her. Alarms should go off, putting Seven on guard.
This admiral knows what her future was like. She remembers that Seven has issues about the return to the AQ and that the C/7 relationship is in its earliest stages. So, she gets Seven alone and attempts to persuade her to disobey her captain's orders. She does this by telling Seven that her death will have a permanent negative impact on her eventual husband, Chakotay. That she is attempting to manipulate Seven is obvious, and Seven would have seen that.
That is, the Seven we have known for four years would have seen it. That Seven would have reported the conversation to the captain and probably would have discussed the news of her possible death with her boyfriend, as well. This news, after all, would not be terribly upsetting to her. Everyone on the crew knows that their lives are in constant danger, so it is something they would have come to terms with long ago. Seven would also know that the admiral's future has forever been changed and that her death is hardly etched in stone. In fact, there is no way to know whether the admiral's story is even true--she could be exaggerating or making it up.
However, this isn't the Seven we've known for four years. This is the naive, impressionable ingenue of "Endgame" who reacts in an immature and illogical way. Not only does she take the admiral's news as gospel, she fails to report this manipuation to the captain, and she doesn't discuss the news of her death with the boyfriend. Nope. She just resigns herself to this future and decides unilaterally to break up with her boyfriend. It's something I'd expect Naomi to do, but not Seven of Nine.
I realize that this is my "reality," but I think it is defensible. I've noticed that you like to defend your reality, too, Teya.
BTW, Guy, I love the "stunt boobies" comment!

It's such a shame that this awesome character had to be packaged in a way that makes her more memorable as a joke than as a serious and interesting person.