My immediate reaction was that they're shitty person too. But I'd also do the same thing anon did and let them have their party.

But are they shitty? It depends how deep is their relationship ig. If she's the one you are going to marry then they're shitty. If the relationship is still in beginning phase, they're kinda like a distant friend and not necessarily needed to be with us in our hard times. I am sure anon's best bro is way closer to anon than his gf.