In shock...

[praying_in_GA]

Does she know what she will do to the entire family if they do this?

Probably not -- "they wouldn't understand" is a common refrain when asked how they would explain the OP to family and friends.

Why would she do this to me?

Selfishness? People who have affairs often describe feeling as if they "deserve" to find happiness outside of their marriage (or by busting up someone else's).

I think *maybe* this could be an EA?? I dunno, he is not talking to me about this so he is talking to her about it. They were pretty close when we started dating. He thought 'be friends with her family and she will follow'.