That sounds like what happened w/ me and XW. We were out at Happy Hour on a Friday and she was moved into my apartment by Sunday.
In hindsight, I'm pretty sure that should have been a sign for me, dont' you think? I can see it all so clearly now and she's repeating this pattern by jumping in w/ her new BF so quickly too.
It is sad how this will affect my D, but I've just got to do the best I can when I'm w/ her and try and minimize the damage.