Tempting as it may have been to throw Sirius out on his ear, Peter couldn't get himself to do it. He was probably sober enough to Apparate or at least hail a cab, but odds were good that he'd climb on his motorbike, go flying somewhere, then fall from a significant height. It would be very ironic indeed to send Sirius off to avoid feeling guilty only for Peter to have his death on his hands.
"Fine." His coat still on, Peter went into the living room and flopped on the sofa. "I'm probably not going to get back to sleep too easily anyway."