You can split a king, don't be such a wimp next time. Though it should totally be assumed that he gets the sofa bed if it's anything smaller. I would, at least as a guest, assume I'm in the sofabed unless otherwise told. But really, I'm happily in a relationship with my girlfriend and if I had a king bed I'd just let someone else sleep in it. It's not like we're going to cop a feel in the middle of the night here.