Ex's and housemates

So I get home from christmassy stuff early this morning, to hear my housemate getting it on with someone. I put the kettle on and ten minutes later my ex comes down the stairs. We've been broken up for over a year, but I was really shocked. We're kinda silent for a fwe minutes and then she says how she wants to get back with me, and how she knows she has probably blown it after this. I tell her its fine. She goes back upstairs. Thirty seconds later I storm out of the house in a huff.
So I've been riding around the last couple of hours, and I just found a place to crash with the interweb. I'm feeling pretty angry and upset with her, but I know that that is pretty irrational considering that we've been broken up for so long (and I broke up with her). He has just confused the hell otu of me. So, is there some kind of social convention for what I should do here? Should I even be feeling angry? And if so, towards who?