Cat waits for those nights alcohol comes through the hatch. It's like she goes in for the kill each and every time.
She has grand delusions of them existing the house hand in hand facing the world and because they stand together it'll be OK. It doesn't change the fact that she has no inkling of consideration for his girlfriend, or the life he'll have to return to, or the stigma they'll now permanently face. They are both so dumb, so disrespectful, so selfish, and so delusional, that maybe they are actually good together.