Say you have a friend. A very dear friend. And one day, he tells you he met someone. And you're all, like, OMG that is so awesome! You encourage your friend and, in trying to show your support for the relationship, establish some kind of virtual connection with the new girl he's seeing. It's all going great: you like her, she likes you, your friend likes her, she likes your friend, you and your friend like each other - it is like the mecca of friendship/love relationships.
And then you decide to hold a birthday party. Only this is a very special birthday party, because it's one of those milestone thingies and you will hold a huge party -- not huge enough that every single contact on your facebook friends list is invited, but huge enough that you are spending all of your savings in said party. Family from around the world is flying in... like, OMG WOW.
Of course your friend is invited -- he is your very best friend, after all. And since you like the girl he is dating, and they are still dating, and she likes you and likes him and it is all a freaking like-fest in this relationship, you invite the girl as well. Only to find out, a couple of weeks after announcing said invitation, that the girl is actually not "in a relationship" with him. Your friend misunderstood her (yeah, because apparently girls have way too many meanings for I love you and stuff) and whereas he thought they were dating (and so informed you), she thought they were just having fun hanging out (doing God-knows-what-when-where-and-how-many-times...).
Your friend hates the witch-with-capital-B, which in turn obviously makes you hate the witch-with-capital-B. But your friend, the idiot that he is, tells you that you should not hate her, because she genuinely likes you, and she is really cool, and that, in retrospect, he did kinda exaggerate things a bit.
If you are any kind of person with feelings now you hate the witch-with-capital-B even more, because not only did the tramp break your friend's heart, she also destroyed his self-confidence.
But -- and here is a BIIIG but... she really is cool (which makes you hate her more!!), and she really does like you. And, in her eyes, the virtual "friendship" that she created with you has nothing to do with your friend. And you two do have a lot in common! And you like her! And she's cool! And she broke your best friend's heart and crushed his self-confidence.
So, in this theoretical situation... what would YOU do?